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To keep a balance in disease specific intestinal insufficiency
Wierdsma, N.J.
2015
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Wierdsma, N. J. (2015). To keep a balance in disease specific intestinal insufficiency: Diagnostics and practical
nutritional aspects.
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To k
eep a b
alanc
e in dise
ase specific Int
estinal Insufficienc
y
Diagnostics and pr actic al nutritional aspectsNic
ole
tt
e Wier
dsma
To keep a balance in disease
specific intestinal insufficiency
Diagnostics and practical nutritional aspects
Nicolette Wierdsma
To keep a balance in disease specific
intestinal insufficiency
Diagnostics and practical nutritional aspects
To keep a balance in disease specific intestinal insufficiency. Diagnostics and practical nutritional aspects
Thesis, VU University Amsterdam, The Netherlands
The research presented in this thesis was performed at the departments of Nutrition and Dietetics, and Gastroenterology of the VU University Medical Center, Amsterdam, The Netherlands.
Printing of this thesis has been financially supported by: Nederlandse Vereniging voor Gastro-enterologie (NVGE), Nederlandse Coeliakie Verenging (NCV), Nederlandse Vereniging van Diëtisten (NVD), ChipSoft BV, Mediq Tefa, Yakult Nederland, Abbott Nutrition, Sorgente, Nestlé Health Science, Danone Research - Centre for Specialised Nutrition, Tramedico BV, Takeda BV Nederland, Fresenius Kabi
Cover: Dennis de Hazen • Grafisch ontwerpbureau De Hazen Lay-out: Ferdinand van Nispen tot Pannerden • Citroenvlinder DTP &
Vormgeving • my-thesis.nl • Bilthoven Printed by: GVO drukkers & vormgevers BV • Ede
ISBN: 978-90-6464-899-1
© 2015 Nicolette J Wierdsma, The Netherlands
VRIJE UNIVERSITEIT
To keep a balance in disease specific
intestinal insufficiency
Diagnostics and practical nutritional aspects
ACADEMISCH PROEFSCHRIFT ter verkrijging van de graad Doctor aan
de Vrije Universiteit Amsterdam, op gezag van de rector magnificus prof.dr. F.A. van der Duyn Schouten,
in het openbaar te verdedigen ten overstaan van de promotiecommissie
van de Faculteit der Geneeskunde op donderdag 12 november 2015 om 13.45 uur
in de aula van de universiteit, De Boelelaan 1105
door
promotor: prof.dr. C.J.J. Mulder
copromotoren: dr. A.A. van Bodegraven
leescommissie: prof dr J (Jon) Shaffer
prof dr EMH (Lisbeth) Mathus-Vliegen
prof dr M (Martin) den Heijer
dr GJA (Geert) Wanten
dr AA (Bert) Beishuizen
dr DL (Donald) van der Peet
paranimfen: dr ir HM (Hinke) Kruizenga
voor Steyn en Matz, mama en papa
Contents
PART ONE GENERAL INTRODUCTION AND OUTLINE OF THE THESIS 11
Chapter 1 Introduction and manuscript content 13
Chapter 2 Case-study: Energetische verliezen uit de korte darm,
meer dan vet alleen
19
Chapter 3 Diagnostic tests for malabsorption and maldigestion 29
PART TWO CLASSICAL METHODOLOGY OF INTESTINAL FUNCTION
IN HEALTH AND DISEASE
Healthy subjects
47
Chapter 4 Bomb calorimetry, the gold standard for assessment
of intestinal absorption capacity: normative values in healthy ambulant adults
Intensive Care Unit
51
Chapter 5 Fecal energy losses in enterally fed intensive care patients:
an explorative study using bomb calorimetry
69
Chapter 6 Malabsorption and nutritional balance in the ICU: fecal
weight as a biomarker: a prospective observational pilot study
Celiac disease
85
Chapter 7 Vitamin and mineral deficiencies are highly prevalent in
newly diagnosed celiac disease patients
105
Chapter 8 Refractory celiac disease and EATL patients show severe
malnutrition and malabsorption at diagnosis
PART THREE ADVANCED ASSESSMENT OF INTESTINAL FUNCTION 147
Chapter 9
Citrulline
Poor diagnostic accuracy of a single fasting plasma citrulline concentration to assess intestinal energy absorption capacity
151
Chapter 10 The citrulline generation test: proposal for a new
enterocyte function test
167
PART FOUR GENERAL DISCUSSION 187
Chapter 11 General discussion and future perspectives 189
PART FIVE ANNEXES 209
Summary Samenvatting Dankwoord List of publications About the author
PART ONE
GENERAL INTRODUCTION
AND OUTLINE OF THE THESIS
Chapter 1
Chapter 1
14
Motive
In 2004, shortly after each other, two patients were admitted to the Gastroenterology and Surgical ward of the VU University Medical Center. Both had active Crohn’s disease due to which they had undergone repeated massive and recurrent small intestine resection. As a consequence, they ended up with a short bowel syndrome, clinically comprising liquid diarrhea, malnutrition (weight loss and vitamin/mineral deficiencies) and need for Total Parenteral Nutrition (TPN).
The question arose whether it would be possible to (completely) wean them from TPN. In other words, whether the absorptive capacity of the remnant small bowel was sufficient to enable reintroduction of full enteral or even oral nutrition. Literature search on intestinal absorptive capacity after radical small bowel surgery and the diagnostic tools to assess absorptive capacity failed to provide an answer to our clinical question.
This induced feelings of insufficiency and disappointment in both patients as well as dietitians and physicians due to lack of appropriate information. The urge to understand the altered absorptive capacity, and possible adaptation, resulted in (re)developing and applying a new ‘old’ method for clinical practice by quantifying fecal nutritional (energy) losses in these patients. It proved to be a labor intensive method, but allowed for a comprehensible and intelligible insight into the ‘accountancy’ of patients’ energy and subsequently their nutritional balances.
The test-derived data, associated with primarily authority-based knowledge of (im)possibilities of the remnant small bowel capacity, provided a basis for further clinical work-up. With the right nutritional (hyperalimentative) supply, education and patients’ motivation, it seemed to be possible to wean both patients from TPN. And appreciatively, it worked out as hoped; nowadays, 10 years later, both patients have a reasonable quality of life, their short bowel function has adapted, and they can manage without TPN.
Introduction and manuscript content
15
1
Outline
The research in this thesis focuses on diagnostic tools and nutritional aspects of patients with or at risk of intestinal failure/intestinal insufficiency. The general aim is to develop valid, reproductive diagnostic test(s) to assess intestinal function in clinical practice for patients at risk of intestinal failure or suffering from intestinal insufficiency. By applying tests to assess digestive function, combined with nutritional assessment tests, we aimed to get a better understanding of pathophysiological aspects (that is measuring of disease-specific consequences for nutritional status) and to improve the (nutrition) treatment and clinical outcome of these patients in future.
This thesis is subdivided into five parts: general introduction with motive and outline of the thesis, studies on classical methodology of gastrointestinal function in health and disease, studies on advanced assessment of intestinal failure by means of citrulline, a general discussion with concluding remarks, and finally annexes with summary, acknowledgements, publications and information about the author.
Part one
Chapter 2 includes a case-study of two intestinal failure patients, being the two described above in chapter 1, showing clinical problems and accountancy on nutritional balance by measuring and reporting energy expenditure, nutritional intake and fecal losses. In chapter 3 an introduction on intestinal failure and (patho)physiology of the gastrointestinal (GI) tract will be provided. Available diagnostic tests for GI function (such as digestion, absorption, motility, assimilation and intestinal barrier) assessment are described and discussed. A clinical algorithm to analyze intestinal function or patients at risk of intestinal failure, is proposed.
Part two
Chapter 1
16
malabsorption in critically ill patients at the Intensive Care Unit are described. In the papers it is shown that malabsorption is an often overlooked problem (‘missed diagnosis’); fecal weight may be used as a biomarker. Chapters 7 and 8 are studies in patients with celiac disease as a model for patients at risk of intestinal failure or intestinal insufficiency. The presence and prevalence of micronutrient deficiencies in celiac disease patients at diagnosis, prior to the treatment with a gluten free diet, are described. Subsequently, both parameters of nutritional status and fecal losses as well as intestinal absorption capacity of patients with a complicated course of celiac disease are displayed.
Part three
Experimental studies on advanced assessment of intestinal function by means of the serum concentration of the amino acid citrulline are described. In chapter 9, the poor diagnostic accuracy of a single fasting plasma citrulline concentration will be described. Fasting plasma citrulline is a poor marker for energy absorption capacity in patients with intestinal failure or intestinal insufficiency, such as patients with Short Bowel Syndrome, (complicated) celiac disease or diffuse enteropathy. In chapter 10, the citrulline generation test is proposed as a new enterocyte function test in which an oral bolus of alanine-glutamine induces a time-dependent rise in plasma citrulline concentration to an extent dependent on the existence of villous atrophy in celiac disease or enterocyte hyperplasia in adapted Short Bowel Syndrome.
Part four
In chapter 11, the main reported findings of our studies are being discussed. Successively, practical implications for diagnostics and treatment of patients (at risk) of intestinal failure in an clinical algorithm, are suggested with, finally, concluding remarks.
Part five
Chapter 2
Case-study:
Energetische verliezen uit
de korte darm,
meer dan vet alleen
Nicolette J Wierdsma and Adriaan A van BodegravenChapter 2
20
Abstract
(Case-study: Energy losses from a short bowel, not only fat)
Case-study
21
2
Dames en Heren,Het korte darm syndroom is een klinisch syndroom dat alle symptomen en pathofysiologische stoornissen omvat na resectie(s) of bypass (in de vorm van een fistel) van een aanzienlijk deel van de dunne darm. De symptomen van het syndroom hebben voornamelijk betrekking op een insufficiënte vertering en absorptie van macro- en micronutriënten en water, zout en galzure zouten, leidend tot gewichtsverlies, diarree, steatorroe, deficiënties van specifieke micronutriënten en (chronische) dehydratie. De mate van verlies van voedingsstoffen en energie verschilt per patiënt en is onder andere afhankelijk van de gereseceerde darmsegmenten, intestinale adaptatie, de aanwezigheid van de ileocoecale klep, de locatie van een stoma of fistels
en eventuele comorbiditeit (1). Het aan te bevelen dieet en de behandeling
zijn eveneens afhankelijk van de aan- of afwezigheid van het colon en de ileocoecale klep, aangezien koolhydraten en in beperkte mate ook eiwitten in het colon geabsorbeerd kunnen worden na bacteriële fermentatie tot
korte keten vetzuren (2-4). De behandeling van patiënten met een korte
darm syndroom is moeilijk en wordt gekenmerkt door een aantal fasen. In de acute fase (circa vier weken na operatie) wordt de patiënt gevoed met totale parenterale voeding (TPV). Op middellange termijn wordt de TPV zo mogelijk gestopt, terwijl de enterale en orale voeding worden opgebouwd. De laatste fase, de lange termijn, wordt doorgaans gekenmerkt door orale voeding, al dan niet met aanvullende enterale voeding en zo nodig specifieke micronutriëntsupplementen.
Aan de hand van 2 casussen laten wij u zien hoe onverwacht groot energetische verliezen kunnen zijn bij patiënten met een korte darm syndroom ten gevolge van aangelegde en spontane fistels.
Chapter 2
22
Tenslotte werd de diagnose ‘exocriene pancreasinsufficiëntie’ gesteld, waarvoor suppletie met pancreasenzymen werd voorgeschreven. Tot dat moment was zijn voeding oraal, aangevuld met 3-4 maal daags orale bijvoeding tot een berekend energetisch totaal van 3500-4250 kcal/dag. Toen patiënt 42 jaar was, zagen wij hem: een inmiddels cachectische, vermoeide en ondervoede man door cumulatief gewichtsverlies in de voorgaande jaren. Het oorspronkelijk gewicht van 100 kg 3 jaar tevoren bij een lengte van 1,87 m (‘body mass index’
(BMI) = 28,6 kg/m2) was gedaald tot 63 kg (BMI = 18,0 kg/m2), dat wil zeggen
Case-study
23
2
Tabel 1: Antropometrische gegevens patiënt A en B
Patiënt Jaartal Leeftijd
(in jaren) Lengte (in m) Gewicht (in kg) BMI (in kg/m2) Gewichtsverlies(in %)
A 2000 39 1,87 100 28,6 2003 42 1,87 63 17,7 38 B 2002 43 1,78 63 19,9 2003 44 1,78 58 50 18,315,8 7,914 (1 mnd) 21 (6 mnd)
Patiënt B is een 45-jarige man met de ziekte van Crohn sedert 24-jarige leeftijd, die een ileocoecale resectie onderging (op 25-jarige leeftijd) en een jejunumresectie (28 jaar), gevolgd door een verwijdingsplastiek (37 jaar). In de loop der jaren werden osteoporose, erythema nodosum en occlusie van de vena centralis retinae gediagnosticeerd. Op 44-jarige leeftijd volgde een hernieuwde verwijdingsplastiek vanwege stenoseklachten met een gecompliceerd postoperatief beloop, leidend tot de aanleg van een hoog jejunostoma. De geschatte resterende dunne darm lengte was ongeveer 180-200 cm. De resterende functionele darm van het type jejunum, als gevolg van de hoog aangelegde fistel, werd geschat op ongeveer 90 cm. Er werd verder geen ontstekings-activiteit van de ziekte van Crohn aangetoond. Een aantal maanden vóór de operatie woog patiënt 63 kg bij een lengte van 1,78 m (BMI
= 19,9 kg/m2). Postoperatief daalde zijn gewicht van 58 kg naar 50 kg (BMI =
15,8 kg/m2) binnen 1 maand tijd, een gewichtsverlies van bijna 14% (zie Tabel
Chapter 2
24
Tabel 2: Voedingsinname, -behoefte en -verlies van patiënt A en B
Patiënt A Patiënt B
Voedingsinname per dag
Aard en hoeveelheid
Energetische waarde (in kcal/dag)
orale en (semi)-elementaire sondevoeding 1500 ml/dag 3800 orale voeding en sondevoeding 1500 ml/dag 5000 Voedingsbehoefte en -verlies
Energiebehoefte* (in kcal/d) Stomaproductie per 2 dagen (in g) Fistelproductie per 2 dagen (in g) Vetverlies via stoma (in g/dag; kcal/d) Energieverlies
Via stoma (kcal/d)^ Via fistel (kcal/d)^
2775 1800 1115 5; 45 550 265 2450 3065 78; 700 2000
Totaal (in kcal/d) 3600 4440
* Gemeten met behulp van indirecte calorimetrie, waarbij een percentage werd opgeteld om te compenseren voor activiteit van patiënt. ^ Gemeten met behulp van bomcalorimetrie.
Deze casuïstiek toont aan dat energetische verliezen via spontane en aangelegde fistels bij patiënten met een functioneel korte darm syndroom niet alleen verklaard worden door vetmalabsorptie. Gezien de grote verschillen in de uitkomsten van de kwantitatieve vetanalyse en de bomcalorische meting lijkt ook het verlies van met name koolhydraten een aanzienlijke bijdrage te kunnen leveren aan het in stand houden van een negatieve energiebalans. Hiervoor dient gecorrigeerd te worden. Een van de mogelijkheden om het energetische verlies via fistels te verminderen of te corrigeren voor verlies, is het gebruik van totale parenterale voeding. Hiervoor zijn duidelijke indicaties
(5). Echter, voor de middellange (>3 maanden na resectie of bypass van de
dunne darm) en lange termijn genieten enterale en orale voeding de voorkeur,
onder andere ter bevordering van de adaptatie (6). Ook gezien de frequent
optredende complicaties van TPV, zoals atrofie van intestinale mucosa en
kathetersepsis, heeft enterale voeding de voorkeur (7-9).
Er is een 10-daagse studie uitgevoerd bij 8 stabiele patiënten met korte darm syndroom met een positieve stikstof-balans naar de absorptiecapaciteit van de dunne darm, door middel van bomcalorimetrie van zowel de voedselinname als de fecale uitscheiding. De gemiddelde energetische absorptie bedroeg 62% (SD: 3), terwijl gezonde personen gemiddeld
meer dan 95% absorberen (10).Opvallenderwijze werd in een andere studie
Case-study
25
2
energetische excretie bij de 25 patiënten met een dunne darm lengte <200 cm en een functionerend colon 620 kcal/dag (SD: 71) (absorptie: 76%), bij de 19 patiënten met 0-100% colon 715 (SD: 71) kcal/dag (absorptie: 66%), en bij de 20 patiënten met een geheel colon 1095 kcal/dag (SD: 119) (absorptie: 55%). Dit in vergelijking met gezonde individuen (>350 cm dunne darm lengte en een volledig colon), die een absorptiecapaciteit van 92-95% hadden en
een verlies van circa 120 kcal/dag via feces (2). Geconcludeerd wordt dat de
energetische inname van deze patiëntengroep verhoogd dient te worden tot
35-40 kcal/kg/dag om verliezen te compenseren (10). Daarentegen adviseerden
andere onderzoekers de energetische inname van oraal gevoede patiënten met korte darm syndroom (tenminste 6 maanden na de resecties), met of zonder colon, met tenminste 50% te verhogen ten opzichte van de normale aanbevelingen, om zo voor de verminderde absorptiecapaciteit
te compenseren (11-12). Tevens wordt aanbevolen voor deze patiëntengroep
en bij gebruik van orale voeding een energetische inname tussen de 120
en 200% ten opzichte van de normale aanbevelingen te bewerkstelligen (13).
Voor een positieve stikstofbalans wordt inname van 80-100 g eiwit per dag
geadviseerd (10). Daarnaast is het bij de behandeling van de patiënt met korte
darm syndroom voor wat betreft de aanbeveling voor vet en koolhydraten belangrijk onderscheid te maken tussen aan- of afwezigheid van het colon, niet alleen in verband met het verlies van water en elektrolyten, maar
evenzeer voor energieabsorptie in het colon door korteketenvetzuren (2, 14).
Aanbevolen voeding voor patiënten met een korte darm syndroom met een functionerend colon is een voeding rijk aan complexe koolhydraten, zoals zetmeel, en arm aan vet, waarmee 30-40% meer energie geabsorbeerd kan worden dan uit een voeding die arm is aan koolhydraten en rijk aan vet, zoals
aanbevolen indien er geen colon meer in situ is (4).
Het nut van de bomcalorimetrie bij patiënten met ernstige absorptiestoornissen
is eerder b eschreven (2). Een van de conclusies van deze studie (n=148) luidde
Chapter 2
26
tweede belangrijke conclusie hing hiermee samen: het meten van alleen de vetexcretie in de feces is een beperkte indicator voor het totale energieverlies in de feces, met name bij patiënten zonder colon, bij wie grote hoeveelheden energie in de vorm van koolhydraten verloren gaan.
Patiënt A had ten tijde van de bomcalorimetrie een energetische absorptie van circa 78%, patiënt B daarentegen slechts 60%. Daarbij was het rustmetabolisme van patiënt A met circa 150 kcal/dag (9%) verhoogd en van patiënt B met circa 250 kcal/dag (17%) ten opzichte van het berekende rust-metabolisme
op basis van de Harris en Benedict-formule (15). Voor zowel een verminderde
absorptiecapaciteit alsmede een verhoogd rustmetabolisme dient gecorrigeerd te worden. Deze uitslagen komen overeen met de aanbevelingen van de
zojuist aangehaalde onderzoekers (11-13) om de energetische inname met circa
50% te verhogen ten opzichte van de normale aanbevelingen (15).
Case-study
27
2
References
1. Buchman AL, Scolapio J, Fryer J. AGA Technical review on short bowel syndrome and intestinal transplantation. Gastroenterology (2003), 124: 1111-1134.
2. Nordgaard I, Hansen BS, Mortensen PB. Importance of colonic support for energy absorption as small-bowel failure proceeds. American Journal of Clinical Nutrition (1996), 64: 222-231.
3. Jeppesen PB, Mortensen PB. The influence of a preserved colon on the absorption of medium chain fat in patients with small bowel resection. Gut (1998), 43: 478-483.
4. Nordgaard I, Hansen BS, Mortensen PB. Colon as a digestive organ in patients with short bowel.
Lancet (1994), 343: 373-376.
5. Gouttebel MC, Saint-Aubert B, Astre C, Joyeux H. Total parenteral nutrition needs in different types of short bowel syndrome. Digestive Diseases and Sciences (1986), 31: 718-723.
6. Sundaram A, Koutkia P, Apovian CM. Nutritional management of short bowel syndrome in adults.
Journal of Clinical Gastroenterology (2002), 34: 207-220.
7. Hernandez G, Velasco N, Wainstein C, Castillo L, Bugedo G, Maiz A, Lopez F, Guzman S, Vargas C. Gut mucosal atrophy after a short enteral fasting period in critically ill patients. Journal of Critical Care (1999), 14: 73-77.
8. Tsujikawa T, Andoh A, Fujiyama Y. Enteral and parenteral nutrition therapy for Crohn’s disease.
Current Pharmaceutical Design (2003), 9: 323-332.
9. Vanderhoof JA, Langnas AN. Short-bowel syndrome in children and adults. Gastroenterology (1997), 113: 1767-1778.
10. Woolf GM, Miller C, Kurian R, Jeejeebhoy KN. Nutritional absorption in short bowel syndrome. Evaluation of fluid, calorie, and divalent cation requirements. Digestive Diseases and Sciences (1987), 32: 8-15.
11. Rodrigues CA, Lennard-Jones JE, Thompson DG, Farthing MJ. Energy absorption as a measure of intestinal failure in the short bowel syndrome. Gut (1989), 30:176-183.
12. Messing B, Pigot F, Rongier M, Morin MC, Ndeïndoum U, Rambaud JC. Intestinal absorption of free oral hyperalimentation in the very short bowel syndrome. Gastroenterology (1991),100: 1502-1508.
13. Wilmore DW, Robinson MK. Short bowel syndrome. World Journal of Surgery (2000), 24: 1486-1492. 14. Nordgaard I. What’s new in the role of colon as a digestive organ in patients with short bowel
syndrome? Nutrition (1998), 14: 468-469.
Chapter 3
Chapter 3
30
Introduction in intestinal failure
Intestinal failure (IF) is nowadays defined as the reduction of gut function below the minimum necessary for the absorption of macronutrients or water and electrolytes, such that intravenous supplementation is required to maintain health or growth. Reduction of gut absorptive function that doesn’t require intravenous supplementation to maintain health and/or growth, can be considered as ‘intestinal insufficiency’. On the basis of onset, metabolic and expected outcome criteria, intestinal failure is classified into three types. Besides it can be classified into five major pathophysiological conditions, which may originate from various gastrointestinal or systemic diseases i.e. short bowel, intestinal fistula, intestinal dismotility, mechanical obstruction
and extensive small bowel mucosal disease (1). As a consequence major
nutritional problems as malnutrition may occur. Malnutrition is, in turn, related to infectious complications, in-hospital duration and morbidity. It has been
stated that adequate nutrition and drug supply, is essential for recovery (2).
For the diagnosis and (nutritional) treatment of IF or intestinal insufficiency, knowledge on (patho)physiology of the gastrointestinal (GI) tract, as well as its assessment, is necessary.
In this chapter, an introduction in GI (patho)physiology will be provided and availability, precision, accuracy, clinical applicability and (dis)advantages of various tests on intestinal function, including digestion, absorption, motility, assimilation or intestinal barrier will be summarized.
(Patho)physiology of the GI tract
PhysiologyThe gut is the largest surface directly interacting between internal and external milieus. It has two major functions: first digestion and absorption of nutrients, and secondly, immune response against a wide variety of antigenic challenges (i.e. forming a selective, semi-permeable intestinal barrier for food components and -other- immunological challenges).
Diagnostic tests for malabsorption and maldigestion
31
3
digestive juices, motility and other pro-secretory functions. Hormonal regulation usually takes place via feedback mechanisms. Additionally, the so-called gut-brain axis refers to the biochemical signaling taking place between the GI tract and the nervous system. This interaction of the gut with the brain is essential for optimal functioning of the GI tract. It comprises symphatic, parasymphatic, and other neuro-intestinal networks. Moreover, biologically active peptides are likely to emerge as neural and endocrine messengers in order to orchestrate the microbiota-gut-brain axis in health and in disease.
Digestion reflects enzymatic conversion of complex dietary substances to an absorbable form, which is initiated by sight, smell or taste of food. In humans, this includes two processes; a mechanical breakdown (oral mastication, chewing, grinding and stomach churning, mixing) and chemical breakdown (action of digestive enzymes, bile acids). The digestive process starts with the production of saliva in the mouth (for complex carbohydrates). It continues in the stomach for proteins by producing hydrochloric acid, which is the catalyst for the conversion of pro-enzym pepsinogen into the active peptide pepsin. Nonetheless, it is primarily the (proximal) intestine that releases digestive enzymes, produced in intestinal organs and the brush border, into the lumen. Absorption comprises the transportation of fluids and (predigested) nutrients across the intestinal mucosa into the body tissues by active transportation, passive or facilitated diffusion, or phagocytosis. It mainly occurs in the villi of the jejunum and ileum.
(Gastrointestinal) Motility, refers to the movement of food from the mouth through the GI tract and per anally out of the body. This coordinated intestinal transport is critically required for a normal functioning GI tract.
Biological assimilation, or bio-assimilation, is the combination of two processes to supply cells with nutrients after digestion and absorption. The first is the process of absorbing vitamins, minerals and other chemicals from food within the GI tract. The second process of bio-assimilation, is the chemical alteration of substances in the bloodstream by liver cells (hepatocytes) or by cellular secretions. Assimilation occurs when the food molecules become part of the body tissues (cells) and therefore it follows the absorption process.
Chapter 3
32
cells separating corporal inside from external environment, i.e. the intestinal contents. By maintaining an intact (electively-permeable) intestinal barrier membrane, pathogenic organisms will be prevented to translocate from the lumen into the body. This is a highly regulated system with inborn and adaptive immune systems which constitutes a complex network of immunoglobulin,
mucus, defensins, and other antimicrobial products (3).
Pathophysiology
A wide array of diseases may alter intestinal physiology, which may result in intestinal dysfunction like maldigestion, malabsorption, dysmotility, malassimilation or increase in intestinal permeability (and, hence, decrease in immune defense). It may therefore induce clinically relevant pathophysiological symptoms like diarrhea or constipation, nausea or vomiting, anorexia, pain, bloating and increased abdominal gas production (eructation, flatulence), heartburn, weight loss, micronutrient deficiencies, impaired immune defense, disbalance of intestinal microbiome, and even life-threatening sepsis. This symptomatology may precede or predict malnutrition secondarily to inadequate nutrient intake, nutrient losses or an accelerated -usually catabolic- metabolism. Maldigestion, defined as an exocrine digestive organ dysfunction leading to insufficient digestion, may occur due to reconstructive or exciding surgery, intestinal fistulas, inflammation (e.g. exocrine pancreatic insufficiency in chronic pancreatitis), decreased gastrointestinal transit time (hypermotility), enterocyte dysfunction (or reduced functional intestinal mass) with subsequent absence of brush border enzymes (like in celiac disease). Maldigestion may be primarily or secondarily, and temporary or chronic by nature. As a consequence, GI complaints and malabsorption may occur.
Malabsorption is defined as a inadequate intestinal absorption of fluid and nutrients. It can occur from diseases that affect the bowels integrity, such as inflammatory diseases of the GI tract (such as Crohn’s disease), Whipple’s disease, celiac disease, oncological treatment (chemotherapy or radiotherapy), or in Intensive Care Unit (ICU) due to Multiple Organ Dysfunction Syndrome, and many others. Malabsorption has been associated with impaired clinical outcomes, such as higher mortality rates, longer hospitalization (for instance ICU) stay and mechanical ventilation, increased morbidity and healthcare costs
(4). In parallel to nutrient malabsorption, absorption of medication may also be
Diagnostic tests for malabsorption and maldigestion
33
3
Dysmotility may comprise both increased (hypermotility) as well as decreased motility (hypomotility) disorders. In case of hypermotility, an accelerated gastro-intestinal transit time occurs, leading to insufficient contact time or uncoordinated or inadequate release of digestive enzymes. In case of hypomotility, intestinal stasis may result with subsequent bacterial overgrowth. Chronic intermittent, intestinal, pseudo-obstruction (CIIP), a relatively frequently missed diagnosis, is characterized by dysmotility with a mixed and alternately clinically apparent motility disorder, but may be chronic and ongoing. Motility disorders are commonly subdivided in the intestinal segments in which these occur: esophagus, stomach, small intestine and colon.
Malassimilation may be a consequence of (a combination of) maldigestion, malabsorption or dysmotility. Reduction of the functional small intestinal area, e.g. following extensive or repetitive intestinal surgery, or radiotherapy in cancer patients, or insufficient mesenterial blood flow in multiple organ dysfunction syndrome patients, results in diminished functional enterocyte mass.
Dysfunction of the intestinal barrier function, usually measured by (increased) intestinal permeability, can be caused by use of antibiotics, toxins, a poor diet, parasites or other infections. A ‘leaky gut syndrome’ may occur as a consequence. GI disorders characterized by malfunction of normal GI activities, but without explaining structural abnormalities, are so-called ‘functional’ GI disorders. There are rarely any tests that can detect the presence of these disorders. Irritable bowel syndrome is considered to be the commonest functional GI disorder.
Assessment of intestinal (patho)physiology
No gold standard, unambiguous and validated test for the various underlying and contributing aspects of intestinal function is available. Yet, several specified or partial intestinal function tests are available, e.g. for detecting or assessing maldigestion, malabsorption, dysmotility, malassimilation (nutrients and intestinal mass) and (changed) intestinal barrier characteristics. Not every test is suitable for each situation and several are only available in research but cannot be used in clinical practice.
Assessment of (mal)digestion
Chapter 3
34
Lundh test - Cholecystokinin (CCK)-secretin test
The Lundh test has been developed to measure the exocrine secretion of pancreatic digestive enzymes. It involves a test meal or hormonal induction (CCK-secretin) to stimulate the pancreas and to aspirate a part of the post-prandial pancreatic secretion (primarily trypsin). This makes it a specific exocrine pancreatic function test. It is operator dependent, time consuming and needs adequate, thus sometimes cumbersome, placement of a duodenal polyethylene
suction tube near the papilla Vateri (5-7). The secretion of pancreatic enzymes
may be decreased due to chronic pancreatic inflammation or obstructive processes (pancreatic cancer). In case of impaired GI transit time or due to digestion coordination problems, pancreatic function may be normal, but its functionality may be decreased, in a digestive way indistinguishable from exocrine dysfunction. The Lundh test is not regularly applied in daily practice. A 24 hours or 72 hours fecal fat content test may also be used, although less specifically, to assess exocrine pancreatic function (see below).
Lactose and fructose hydrogen breath tests
A disaccharide (lactose or fructose) intolerance is a common GI disorder, meaning that a subject has abdominal complaints due to lack of (functional) enzymes (maltase, isomaltase, lactase or fructase). However, (secondary) lactase deficiency is the most common disaccharidase deficiency, whereas fructase deficiency is rare. The principle of the breath test is that a subject ingests a fixed amount of the investigated disacharide, which remains undigested in the small intestine, and reaches the colon undigested. There, it is acted on and fermented by anaerobic colonic bacteria, producing hydrogen, which is subsequently absorbed and finally exhaled via the lungs. The exhaled breath is to be captured and analyzed at various time points following ingestion. Hydrogen breath test following ingestion of 50 g of lactose (or 20 g fructose), although associated with GI-symptoms, has been shown to have a higher sensitivity and specificity,
if compared to the gold standard method (mucosal biopsy lactase activity)
(8-10). Studies with 25 g dose lactose are showing acceptable test characteristics.
Breath tests are relatively easy to perform and predictive for enzyme deficiency,
or disaccharide intolerance. Moreover breath tests (with glucose, lactose or (13C)
Diagnostic tests for malabsorption and maldigestion
35
3
20 ppm of hydrogen and/or methane within the first two hours (indicating bacteria in the small intestine) and followed by a much larger peak, indicating the colonic response. Flaws of the test comprise, among others, failed fasting, concurrent smoking, constipation and methane producing fermenting bacteria instead of H2-producers.
Assessment of (mal)absorption
Intestinal losses can be quantified by measurement of fecal (unabsorbed) nutrients. Consecutively, specific fecal tests for fat, protein and energy will be discussed. For carbohydrates, no appropriate, easily accessible (or feasible) test is available.
Assessment of fat (mal)absorption Fecal fat excretion test
Classically, fecal fat content can be measured chemically and quantified by the van de Kamer-method. Collected feces of several days (preferably 3-7), usually in combination with a pretest period of 4-7 days for consumption of a diet saturated
with a known, or standardized amount of fat (11). The intestinal absorption
capacity of fat can be calculated by extracting fecal fat from ingested fat and expressed as a percentage of ingested fat. The underlying concept of the fecal fat excretion test is that the malabsorption of fat correlates with malabsorption in general (11). It should be realized, however, that fat-malabsorption reflects only
to a certain extent the total absorptive capacities of the intestine. Qualitative fecal fat screening
In a qualitative and semi-quantitative way, fecal fat can be demonstrated with Sudan III staining. By using Sudan III solution, the fat (and fatty acids) actually present in feces, will be colored (orange) after heating. The amount of fat is scored semi-quantitatively, and therefore this method is most commonly used as a rough estimate or screening tool.
Triolein-lipid absorption test
Chapter 3
36
and specificity, when using a small fat load (20 g). It can also be performed with the stable 13C carbon isotope (12-15).
Assessment of protein (mal)absorption Fecal nitrogen excretion test
Unabsorbed protein can be estimated by quantifying fecal nitrogen content (Kjehdahl technique), multiplied by 6.25 for conversion into proteins. In this method, all the excreted nitrogen is interpreted as residues of endogenous ingested protein, while this is partly derived from intestinal leakage, shredded
cells, bacteria and others (16). No link is made with ingested protein from
nutritional intake, so, in its current form, it does not reflect intestinal protein absorption.
Radio actively labeled protein test
In research setting, labeled isotope techniques are used to study protein absorption and metabolism. By combining the use of specifically produced
intrinsically L-[1-13C]phenylalanine-labeled dairy protein with continuous
intravenous L-[ring-2H5]phenylalanine infusion, in vivo dietary protein digestion
and absorption kinetics can be assessed (17,18). Rarely, radio actively albumin is
used to assess protein malabsorption, since protein malabsorption induces a decrease in albumin synthesis rate (19-20).
Fecal alpha-1 antitrypsine (clearance)
The protein fecal alpha-1 antitrypsine is a non-digestable protein and can be measured in feces and serum. Subsequently, clearance can be calculated as a marker for the amount of intestinal protein loss. It is mostly used as a diagnostic test for intestinal protein leakage or diagnosing protein losing enteropathy rather than it is a malabsorption test (14).
Assessment of fecal energy content Bomb calorimetry
Diagnostic tests for malabsorption and maldigestion
37
3
the (putative) gold standard for quantifying intestinal energy losses (21, 22).But
by assessing only the intestinal output, it is not a sensitive marker for intestinal absorption, since bomb calorimetry per se is not related to nutritional intake in the feces collection period.
D-xylose absorption test
The D-xylose test is an indicator of overall nutrient absorption. By oral administration of the monosaccharide D-xylose, small intestinal absorption can be quantified. D-xylose is transported across the intestinal epithelium (jejunum) by a passive, carrier mediated pathway. The standard oral dose for adults is 25 g of D-xylose. To measure intestinal absorption, the following three specimens can be used: breath, urine, or blood. Approximately 50% of an intravenous dose is recovered in the urine. Furthermore, breath tests with
D-xylose as substrate, including the hydrogen, 13C-D-xylose, and 14C-D-xylose
breath test, are all available. Breath tests are often used for diagnosing bacterial overgrowth, relying on breakdown of the non-absorbed sugars by intestinal flora. In healthy individuals, the usual lower reference limit of the 5 hour urine test is 4 g, using a standard dose of 25 g D-xylose. For the 1 hour blood test, the putative lower reference limit is 25 mg/dL (15, 23-27).
Assessment of (dys)motility
In clinical practice, manometry remains one of the most important investigational techniques for gastrointestinal (dys)motility, in particular for esophageal, gastroduodenal and anorectal disorders. Yet, scintigraphy still is the gold standard for assessment of gastric emptying in clinical practice, manometry and
13C breath tests being alternatives, mostly in research. Many other techniques
are being used mainly in the context of scientific research of which only some
may become incorporated in the diagnostic armamentarium (28, 29).
Assessment of (mal)assimilation
Chapter 3
38
Fasting citrulline
In the last decade, the semi-essential amino acid citrulline, measured by using reverse-phase high-performance liquid chromatography (HPLC), has been proposed as an attractive marker to assess small intestinal function indirectly. Since citrulline is almost entirely produced from conversion of glutamine in (mainly proximal small bowel) enterocytes, its plasma level is reported to correlate with the (total) enterocyte mass and functional small bowel length. Decreased fasting plasma citrulline concentrations are detected in patients with small bowel atrophy or other destructive villous lesions like celiac disease, short
bowel syndrome, HIV positive or infectious disease patients (30-34).But studies
are lacking in patients with intestinal insufficiency or relation with intestinal absorption.
Intestinal barrier function tests
Intestinal barrier function can be assessed by intestinal permeability measurements. Intestinal permeability for larger molecules (macromolecules of 12000-15000 Da) reflects the functional integrity of the mucosa of the small bowel (35, 36). Permeability tests are based on the intestinal passage of a solute by
unmediated diffusion, which is determined by the structure of the membrane, e.g. composition, charge and thickness, as well as the physicochemical properties of the solute, such as molecular size, shape, charge and solubility, and its interaction with the solvent. Normally, molecules up to the size of monosaccharides, such as mannitol (MW of 182 Da), are believed to use the transcellular route, and disaccharides (like lactulose with a MW 342 Da) or larger molecules are believed to be transported through the paracellular route across the intestinal wall. So permeability for small (mono) saccharides (<0.5 nm f.i. rhamnose, alcohol or mannitol), is higher than for larger (>0.5 nm f.i. di- or poly) saccharides. Under pathological conditions, intestinal permeability for small saccharides does not change or decreases and increases for larger saccharides, which results in an increase in the ratio of large to small sugars (36).Two different
test will be discussed below (SAT and PEG). Sugar absorption test (SAT)
Diagnostic tests for malabsorption and maldigestion
39
3
available to reduce test variation, since all sugars are likely to be affected by non-mucosal factors in a similar way and it has better test accuracies on intestinal
permeability than the classical dual-sugar tests (36-43).Subsequently, urinary
excretion of saccharides (particularly the large saccharide/ small saccharide ratio) is measured being a marker for damaged intestinal barrier function (leakage), and may be a derivative method to indicate small bowel absorptive function. Intestinal permeability tests for saccharides. SAT tests are integrated as permeability test in clinical practice and research settings and seems most suitable for clinical purposes, because they are simple and noninvasive. Although SAT test cannot be used in case of oliguria, anuria or in multiple organ failure in ICU patients due to the various non-permeability-related confounders such as impaired renal function (44).
Polyethylene glycol (PEG) test
Similarly to the SAT test, permeability assessment with PEG’s are available (with different sizes such as PEG 400, 600, 900, 1000, 3000 and 4000, the first being used most frequently). PEG is orally administered after an overnight fast with a fixed volume of water. Afterwards, urine specimens are collected for 5-6 hours for analysis. By determination of urinary PEG excretion or by calculation of urine excretion ratios of the various polymers intestinal permeability can be quantified
(45).Similar to qualitative feces tests, the PEG test is also more a screening tool
than of great diagnostic value. It seems not sufficiently sensitive to assess intestinal permeability in more subtle disorders of barrier function. Moreover, analysis of PEG is time consuming and technically challenging; therefore PEG test is less suitable for clinical practice.
Clinical applicability
Chapter 3
40
protocol, and lack of knowledge and priority. But, nevertheless, quantitatively fecal analyses are feasible and reproducible in clinical practice. Since it is not recommended to use the quick and simple qualitative tests on feces portion (for instance fecal fat) instead of quantitatively based fecal tests due to the low diagnostic value (false positive or false negative results), more elaborative 24 hours of 72 hours fecal collection tests are being recommended.
When tests require urine collection (like D-xylose, SAT or PEG tests), similar problems and pitfalls arise as in feces collection tests; it is logistically challenging to obtain an accurately timed and adequate urine specimen collection, especially in very young children, infants, and disabled ones.
Some GI function tests are based on breath tests (like lactose and fructose hydrogen breath test), which allows for accurate diagnoses in a wide variety of clinical situations, such as dyspepsia, eradication of bacteria, diarrhea, post-surgical syndromes and more. These are non-invasive and exploit normal (physiological) principles of intestinal gas dynamics and the action of bacteria on different substrates. (Urease) radioactive isotope tests (like hydrogen of stable carbon), seem sensitive, specific and save, but these are more expensive and technically challenging (24).
Clinical approach in intestinal failure; missing links
No single test is sufficiently accurate to diagnose or assess overall gastrointestinal function in health or disease GI function, among which digestion and absorption (including motility and assimilation) as well as intestinal barrier function. Since small bowel dysfunction is present in a variety of GI diseases, measurement of intestinal (remaining) function is of critical clinical value for diagnosis, treatment, follow up and evaluation of disease severity and course.
Diagnostic tests for malabsorption and maldigestion
41
3
Patient at risk of intestinal failure
Baseline screening and assessment (physical
, anamnesis
, medication
)
Focus on specific intestinal function
Digestion GI -motility Absorption Assimilation Intestinal barrier (P ) Lactose /fructose
hydrogen breath test
(S
) Quantitative fecal analysis
(fat , nitrogen , bomb calorimetry ) (S ) D
-Xylose absorption test
(S ) Alpha -1 antitrypsine (E ) Triolein
-lipid absorption test
(E
) Radio actively labelled protein test
P = preference S = second best E = exception (P ) Manometry (P ) Scintigraphy (S ) 13C breath test (S ) Fasting citrulline (P
) Sugar absorption test
Chapter 3
42
References
1. Pironi L, Arends J, Baxter J, Bozzetti F, Peláez RB, Cuerda C, Forbes A, Gabe S, Gillanders L, Holst M, Jeppesen PB, Joly F, Kelly D, Klek S, Irtun Ø, Olde Damink SW, Panisic M, Rasmussen HH, Staun M, Szczepanek K, Van Gossum A, Wanten G, Schneider SM, Shaffer J. Home Artificial Nutrition & Chronic Intestinal Failure and the Acute Intestinal Failure Special Interest Groups of ESPEN. ESPEN endorsed recommendations. Definition and classification of intestinal failure in adults. Clinical
Nutrition (2015), 34 (2): 171-180. doi: 10.1016/j.clnu.2014.08.017.
2. Martindale RG, McClave SA, Vanek VW, McCarthy M, Roberts P, Taylor B, Ochoa JB, Napolitano L, Cresci G; American College of Critical Care Medicine; ASPEN Board of Directors. Guidelines for the provision and assessment of nutrition support therapy in the adult critically ill patient: Society of Critical Care Medicine and American Society for Parenteral and Enteral Nutrition: Executive Summary. Critical Care Medicine (2009), 37 (5): 1757-1761. doi: 10.1097/CCM.0b013e3181a40116. 3. Arrieta MC, Bistritz L, Meddings JB.Alterations in intestinal permeability. Gut (2006), 55 (10):
1512-1520.
4. Reintam A, Parm P, Redlich U, Tooding LM, Starkopf J, Köhler F, Spies C, Kern H. Gastrointestinal failure in intensive care: a retrospective clinical study in three different intensive care units in Germany and Estonia. BMC Gastroenterology (2006), 6: 19.
5. Beck IT. Diagnosis of chronic pancreatic disease. Clinical Biochemistry (1976), 9 (3): 121-130. 6. James O. The Lundh test. Gut (1973), 14 (7): 582-591.
7. Herskovic T. The exocrine pancreas in intestinal malabsorption syndromes. American Journal of
Clinical Nutrition (1968), 21 (5): 520-522.
8. Newcomer AD, McGill DB, Thomas PJ, Hofmann AF. Prospective comparison of indirect methods for detecting lactase deficiency. New England Journal of Medicine (1975), 11; 293 (24): 1232-1236. 9. Hoekstra JH, van Kempen AA, Bijl SB, Kneepkens CM. Fructose breath hydrogen tests. Archives of
Diseases in Childhood (1993), 68 (1): 136-138.
10. Kneepkens CM, Vonk RJ, Fernandes J. Incomplete intestinal absorption of fructose. Archives of
Diseases in Childhood (1984), 59 (8): 735-738.
11. Van de Kamer JH, ten Bokkel Huinink H, Weyers HA. Rapid method for the determination of fat in feces. Journal of Biological Chemistry (1949), 177 (1): 347-355.
12. See comment in PubMed Commons belowMundlos S, Kühnelt P, Adler G. Monitoring enzyme replacement treatment in exocrine pancreatic insufficiency using the cholesteryl octanoate breath test. Gut (1990), 31 (11): 1324-1328.
13. Watkins JB, Schoeller DA, Klein PD, Ott DG, Newcomer AD, Hofmann AF. 13C-trioctanoin: a nonradioactive breath test to detect fat malabsorption. Journal of Laboratory and Clinical Medicine (1977), 90 (3): 422-430.
14. Strygler B, Nicar MJ, Santangelo WC, Porter JL, Fordtran JS. Alpha 1-antitrypsin excretion in stool in normal subjects and in patients with gastrointestinal disorders. Gastroenterology (1990), 99 (5):1380-1387.
15. Papadia C, Di Sabatino A, Corazza GR, Forbes A. Diagnosing small bowel malabsorption: a review.
Internal and Emergency Medicine (2014), 9 (1): 3-8. doi: 10.1007/s11739-012-0877-7.
16. Rudman D, Millikan WJ, Richardson TJ, Bixler TJII, Stackhouse WJ, McGarity WC. Elemental balances during intravenous hyperalimentation of underweight adult subjects. Journal of Clinical
Investigation (1975), 55: 94-104.
17. Pennings B, Pellikaan WF, Senden JM, van Vuuren AM, Sikkema J, van Loon LJ. The production of intrinsically labeled milk and meat protein is feasible and provides functional tools for human nutrition research. Journal of Dairy Sciences (2011), 94 (9): 4366-4373. doi: 10.3168/jds.2011-4451. 18. van Loon LJ, Boirie Y, Gijsen AP, Fauquant J, de Roos AL, Kies AK, Lemosquet S, Saris WH, Koopman R.
The production of intrinsically labeled milk protein provides a functional tool for human nutrition research. Journal of Dairy Sciences (2009), 92 (10): 4812-4822. doi: 10.3168/jds.2009-2317. 19. Klein S. The myth of serum albumin as a measure of nutritional status. Gastroenterology (1990), 99
Diagnostic tests for malabsorption and maldigestion
43
3
20. Waldmann TA, Wochner RD, Strober W. The role of the gastrointestinal tract in plasma proteinmetabolism. Studies with 51Cr-albumin. American Journal of Medicine (1969), 46 (2): 275-285. 21. Lovelady HG, Stork EJ. An improved method for preparation of feces for bomb calorimetry. Clinical
Chemistry (1970), 16 (3): 253-254.
22. Miller DS, Payne PR. A ballistic bomb calorimeter. British Journal of Nutrition (1959),13: 501-508. 23. Helmer OM, Fouts PJ. Gastro-intestinal studies VII. The excretion of xylose in pernicious anemia.
Journal of Clinical Investigation (1937), 16 (3): 343-349.
24. Romagnuolo J, Schiller D, Bailey RJ. Using breath tests wisely in a gastroenterology practice: an evidence-based review of indications and pitfalls in interpretation. American Journal of
Gastroenterology (2002), 97 (5): 1113-1126.
25. Breiter HC, Craig RM, Levee G, Atkinson AJ Jr. Use of kinetic methods to evaluate D-xylose malabsorption in patients. Journal of Laboratory and Clinical Medicine (1988), 112 (5): 533-543. 26. Worwag EM, Craig RM, Jansyn EM, Kirby D, Hubler GL, Atkinson AJ Jr. D-xylose absorption and
disposition in patients with moderately impaired renal function. Clinical Pharmacological Therapy (1987), 41 (3): 351-357.
27. Craig RM, Murphy P, Gibson TP, Quintanilla A, Chao GC, Cochrane C, Patterson A. Atkinson AJ Jr. Kinetic analysis of D-xylose absorption in normal subjects and in patients with chronic renal failure.
Journal of Laboratory and Clinical Medicine (1983), 10 1 (3): 496-506.
28. Smout AJ, Mundt MW. Gastrointestinal motility testing. Best Practice and Research Clinical
Gastroenterology (2009), 23 (3): 287-298. doi: 10.1016/j.bpg.2009.04.006.
29. Keller J, Layer P. Intestinal and anorectal motility and functional disorders. Best Practice and Research
Clinical Gastroenterology (2009); 23 (3): 407-423. doi: 10.1016/j.bpg.2009.02.012.
30. Crenn P, Messing B, Cynober L. Citrulline as a biomarker of intestinal failure due to enterocyte mass reduction. Clinical Nutrition (2008), 27 (3): 328-339. doi: 10.1016/j.clnu.2008.02.005.
31. Crenn P, Vahedi K, Lavergne-Slove A, Cynober L, Matuchansky C, Messing B. Plasma citrulline: A marker of enterocyte mass in villous atrophy-associated small bowel disease. Gastroenterology (2003), 124 (5): 1210-1219.
32. Pappas PA, Saudubray JM, Tzakis AG, Rabier D, Carreno MR, Gomez-Marin O, Huijing F, Gelman B, Levi DM, Nery JR, Kato T, Mittal N, Nishida S, Thompson JF, Ruiz P. Serum citrulline as a marker of acute cellular rejection for intestinal transplantation. Transplantation Proceedings (2002), 34 (3): 915-917.
33. Rhoads JM, Plunkett E, Galanko J, Lichtman S, Taylor L, Maynor A, Weiner T, Freeman K, Guarisco JL, Wu GY. Serum citrulline levels correlate with enteral tolerance and bowel length in infants with short bowel syndrome. Journal of Pediatrics (2005), 146 (4): 542-547.
34. Luo M, Fernández-Estívariz C, Manatunga AK, Bazargan N, Gu LH, Jones DP, Klapproth JM, Sitaraman SV, Leader LM, Galloway JR, Ziegler TR. Are plasma citrulline and glutamine biomarkers of intestinal absorptive function in patients with short bowel syndrome? Journal of Parenteral and
Enteral Nutrition (2007), 31 (1): 1-7.
35. van Elburg RM, Kokke FT, Uil JJ, Mulder CJ, de Monchy JG, Heymans HS. Measurement of selective intestinal permeability using a new, simple sugar absorption test. Nederlands Tijdschrift voor
Geneeskunde (1993), 137 (41): 2091.
36. van Elburg RM, Uil JJ, Kokke FT, Mulder AM, van de Broek WG, Mulder CJ, Heymans HS. Repeatability of the sugar-absorption test, using lactulose and mannitol, for measuring intestinal permeability for sugars. Journal of Pediatric Gastroenterology and Nutrition (1995), 20 (2): 184-188.
37. Keur MB, Beishuizen A, van Bodegraven AA. Diagnosing malabsorption in the intensive care unit.
F1000 Medicine Reports (2010), 27; 2. pii: 7. doi: 10.3410/M2-7.
38. Hessels J, Eidhof HH, Steggink J, Roeloffzen WW, Wu K, Tan G, van de Stadt J, van Bergeijk L. Assessment of hypolactasia and site-specific intestinal permeability by differential sugar absorption of raffinose, lactose, sucrose and mannitol. Clinical Chemistry and Laboratory Medicine (2003), 41 (8): 1056-1063.
Chapter 3
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40. Tveito K, Brunborg C, Bratlie J, Askedal M, Sandvik L, Lundin KE, Skar V. Intestinal malabsorption of D-xylose: comparison of test modalities in patients with celiac disease. Scandinavian Journal of
Gastroenterology (2010), 45 (11): 1289-1294. doi: 10.3109/00365521.2010.503969.
41. Peled Y, Doron O, Laufer H, Bujanover Y, Gilat T. D-xylose absorption test. Urine or blood? Digestive
Diseases and Sciences (1991), 36 (2): 188-192.
42. Braden B, Lembcke B, Kuker W, Caspary WF. 13C-breath tests: current state of the art and future directions. Digestive and Liver Diseases (2007), 39 (9): 795-805.
43. Casellas F, Chicharro L, Malagelada JR. Potential usefulness of hydrogen breath test with D-xylose in clinical management of intestinal malabsorption. Digestive Diseases and Sciences (1993), 38 (2): 321-327.
44. Oudemans-van Straaten HM, van der Voort PJ, Hoek FJ, Bosman RJ, van der Spoel JI, Zandstra DF. Pitfalls in gastrointestinal permeability measurement in ICU patients with multiple organ failure using differential sugar absorption. Intensive Care Medicine (2002), 28 (2): 130-138.
PART TWO
CLASSICAL METHODOLOGY
OF INTESTINAL FUNCTION
IN HEALTH AND DISEASE
Chapter 4
Bomb calorimetry, the gold
standard for assessment
of intestinal absorption
capacity: normative values
in healthy ambulant adults
Nicolette J Wierdsma, Job H Peters, Marian AE van Bokhorst-de van der Schueren, Chris JJ Mulder, Ingrid Metgod and Adriaan A van Bodegraven
Chapter 4
52
Abstract
Background: Intestinal absorption capacity is considered to be the best method for assessing overall digestive intestinal function. Earlier reference values for intestinal function in healthy Dutch adults were based on a study that was conducted in an inpatient metabolic unit setting in a relatively small series. The present study aimed to readdress and describe the intestinal absorption capacity of healthy adults, who were consuming their usual (Western European) food and beverage diet, in a standard ambulatory setting.
Methods: Twenty-three healthy subjects (aged 22-60 years) were included in the analyses. Nutritional intake (energy and macronutrients) was determined with a four-day nutritional diary. Subsequently, mean fecal losses of energy (by bomb calorimetry), fat, protein and carbohydrate were determined following a 3-day fecal collection. Finally, intestinal absorption capacity was calculated from the differences between intake and losses.
Results: Mean (± SD) daily feces production was 141 ± 49 g (29% dry weight), containing 213 ± 66 kcal (1.6 ± 0.3 kcal/g wet feces; 5.4 ± 0.6 kcal/g dry feces), 5.2 ± 2.2 g fat, 10.0 ± 3.8 g protein and 29.7 ± 11.7 g carbohydrates. Mean intestinal absorption capacity of healthy subjects was 89.4 ± 3.8% for energy, 92.5 ± 3.7% for fat, 86.9 ± 6.4% for protein and 87.3 ± 6.6% for carbohydrates.
Bomb calorimetry; intestinal absorption in healthy adults
53
4
Introduction
The absorption of nutrients is an essential function of the gastrointestinal tract, notably of the small intestine. In humans, it is proposed that absorption can be used as a surrogate measure for the whole process of digestion. Absorption is a major physiological function of the intestine. Hence, intestinal absorption
capacity may be used as a semi-quantitive marker of intestinal function (1).
Clinically evident malabsorption is an issue encountered in daily practice. It is a major clinical challenge when intestinal failure (IF), as defined in accordance
with the recently updated definitions (2), has been diagnosed. Intestinal
failure may be observed in a wide array of clinical problems and is regularly encountered in general and referral hospitals. Intestinal failure is common in, for example, intensive care unit patients (3, 4), radiation enteritis after surgical
treatment, Crohn’s disease and other chronic inflammatory intestinal diseases, such as autoimmune enteropathy and refractory coeliac disease. It may lead to a negative balance of energy and proteins, dehydration, deficiencies of vitamins, minerals or trace elements, and a decreased quality of life. In these IF patients, knowledge of intestinal function, as measured by intestinal absorptiometry, is essential. This comprises relevant information with respect to providing adequate dietary advice that aims to adjust to the medical and nutritional care needs of individual patients. In addition, it allows follow-up of the digestive capacity in a quantitative manner. If necessary, it can also be performed regularly until dietetic balance is secured.
Bomb calorimetry, in which fecal energy content is measured by heat of combustion, is regarded as the gold standard laboratory method for quantifying
energy losses (5, 6). Bomb calorimetric measurements may be of clinical importance
for the early recognition of patients with malabsorption as a consequence of IF. Calculating intestinal absorption as the difference between nutritional intake and fecal losses (as a percentage of the nutritional intake) is a widely accepted
method (1, 7-10). It is generally regarded to be the quantitative gold standard
for digestion or intestinal function in clinical practice, being an undisputed biomarker of gastrointestinal functionality. Furthermore, measurement of fecal macronutrient losses can be of additional value in diagnosing and interpreting malabsorptive signs.
Chapter 4
54
the usual circumstances for dietetic and nutritional interventions or therapy. Based on a small study conducted in an inpatient metabolic unit setting, ‘standard’ energy absorption is estimated to be at a level of 95% because non-absorbed energy in healthy adults has been reported to be approximately 5% when digesting a standard diet (11).
For reasons of practical applicability, the present study aimed to assess fecal energy, subdivided in its major contributors of fat, protein and carbohydrate losses, to quantify standard intestinal absorption capacity in healthy adults on a Western European diet in an ambulatory setting in The Netherlands by using a feasible and unique methodology of intestinal absorptiometry reflecting routine practice.
Materials and methods
SubjectsTwenty-five healthy subjects participated in the present study. Subjects were mainly institutional healthcare workers with specific dietetic and healthcare knowledge. Therefore, they were selected as having skilled competence in adequately registering nutrient intake and meticulously collecting stools. Inclusion was based on voluntary enrolment. The subjects had to meet certain criteria:
• Healthy, defined as absence of gastrointestinal diseases or abnormalities, current or common disease, eating disorders or pregnancy;
• Age 18 years;
• Regular bowel habits;
• No concomitant use of antibiotics or medication interfering with gastrointestinal motility and;
• Exclusively orally fed without dietary restrictions.
The medical ethical committee of VU University Medical Center, Amsterdam approved the study protocol and written informed consent was obtained from all subjects.
Methods
Bomb calorimetry; intestinal absorption in healthy adults
55
4
collected during the final 3 days. For urinary protein losses, a standardized and fixed correction factor for healthy people, with normal kidney function, was taken into account (11). Subjects collected the data and stools at home in the predefined
period, during which they were obliged to continue their habitual diet. Food and beverage intake
An experienced and dedicated dietitian (NJW) instructed all subjects in advance with respect to accurately weighing all food and drinks using digital electronic scales and recording information, such as brand names, next to cooking methods, if any, for all foods and beverages during the study period. Additionally, the same dietitian interviewed all subjects afterwards to ensure adequate documentation and to check whether all study procedures had been complied with. A computerized food calculation programme (based on the
National Dutch Food Composition Table ‘NEVO’ 2006) (12) was used to calculate
mean nutrient intake (fat, protein and carbohydrates). The total energy intake (TEI) of the diet was determined by using the gross energetic values for fat (9.40 kcal/g), protein (4.40 kcal/g, derived from the gross energetic value of 5.65 kcal/g protein minus the fixed correction for urinary nitrogen loss of 1.25
kcal/g (13) and carbohydrates (4.10 kcal/g), multiplied by the amount supplied.
Nutrient losses
All feces were collected during 72 hours (day 2-4), as per the protocol, in specifically designed 5-L buckets. Feces were weighed (fecal wet weight in g/d), homogenized and immediately stored at <4°C until analysis. To measure fecal macronutrient content and to calculate intestinal absorption capacity of the healthy subjects, the feces were analyzed for energy, fat and nitrogen content.
The fecal fat content (FFat) was determined by the method of Van de Kamer (14).
On a sample of wet stools, total nitrogen analysis was performed using the
micro-Kjeldahl method to determine fecal nitrogen content (FNitrogen) using
previously described catalytic and digestive conditions (15). Fecal protein (F Protein)
was calculated using a conversion factor, assuming that all of the FNitrogen was
Chapter 4
56
steel bomb, water, a stirrer, a thermometer, the dewar or insulating container (to prevent heat flow from the calorimeter to the surroundings) and an ignition circuit connected to the bomb. The temperature change in the water is accurately measured with a thermometer, and so it is used to calculate the energy given out by the sample burned (in this case, feces) (5, 6).These calorimetric determinations
represented daily fecal energy loss (FEnergy) in kcal/d and were performed using
a Ballistic bomb calorimeter, (type CBB-33; Gallenkamp Manufactory, EttenLeur, The Netherlands) at the University of Groningen, The Netherlands. Finally, fecal
carbohydrate content (FCarbohydrate) was calculated from the nonfat, nonprotein
and nonwater fraction of stools (i.e. the fecal ‘remaining’) and was calculated using the formula: FCarbohydrate (g/d) = (FEnergy - FFat x 9.4 - FProtein x 4.4)/4.10. The intestinal absorption capacity (%) of ingested energy from macronutrients was finally calculated as: (TEI - FEnergy/TEI) x 100. Specific intestinal malabsorption of energy, fat, protein and carbohydrate was a priori defined as an absorption capacity of 85% or less (1, 11).
Statistical analysis
Data obtained from 2 subjects were excluded from the data analyses as a result of incomplete data collection. The data for the remaining 23 subjects are presented as the mean (SD), either range or 95% confidence interval (CI), and box and whisker plots. Subject groups were compared using Students’ t-test and analysis of variance in the case of more than two groups. Associations between variables were evaluated by Pearson’s correlation coefficient (r) and the chi-squared test, where appropriate. P<0.05 was considered statistically significant. Outliers were defined as values >3 SD. Statistical analysis were carried out using SPSS, version 18 (SPSS Inc., Chicago, IL, USA). Data were analyzed for the total group and separately for men and women.
