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The diagnosis and prognosis of venous thromboembolism : variations on a
theme
Gibson, N.S.
Publication date
2008
Link to publication
Citation for published version (APA):
Gibson, N. S. (2008). The diagnosis and prognosis of venous thromboembolism : variations
on a theme.
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Validityandclinicalutilityofthe
simplifiedWellsruleforassessingclinical
probabilityofpulmonaryembolism
RENÉEA.DOUMA,NADINES.GIBSON,VICTORE.A.GERDES,HARRYR.BÜLLER, PHILIPS.WELLS,ARNAUDPERRIER,GRÉGOIRELEGAL
SUBMITTED
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A
BSTRACT
Background
Clinical decision rules are used to objectively assess clinical probability of pulmonary embolism (PE). The recently introduced simplified Wells rule assigns only one point to the seven variables of the original Wells rule. This study was performedtoindependentlyvalidatethesimplifiedWellsrule.
Methods
We retrospectively calculated the prevalence of PE in the unlikely probability categoriesoftheoriginalWells(cutoff4)andthesimplifiedWellsrule(cutoff 1) in 922 consecutive patients with clinically suspected PE from a multicenter cohort study. We compared the 3month incidence of venous thromboembolism (VTE) in patients with an unlikely probability and a normal Ddimer test using bothscores,andtheproportionofpatientswiththiscombination(clinicalutility).
Results
The proportion of patients categorized as PE unlikely was similar using the original(78%)andthesimplified(70%)Wellsrule.TheprevalenceofPEwas13% (95% confidence interval [CI] 1116%) for the original Wells “unlikely” category and12%(95%CI9.715%)forthesimplifiedWells“unlikely”category.Noneofthe patientswithPE“unlikely”andanormalDdimertestexperiencedVTEduring3 month followup. The proportions of patients in whom further tests could safely be withheld based on “PE unlikely” combined with a normal Ddimer test was 28% (95%CI 2531%) for the original score and 26% (95%CI 2429%) using the simplifiedWellsrule.
Conclusions
Inthisexternalvalidationstudy,thesimplifiedWellsruleappearedtobesafeand clinicallyuseful.SimplificationoftheWellsrulemayenhancetheapplicability.
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I
NTRODUCTION
Many diagnostic algorithms for patients with clinically suspected pulmonary embolism (PE) have been investigated for their safety and utility. Due to the low prevalence of pulmonary embolism, confirming the diagnosis in the minority of patientswhohavethedisease,whilesafelyexcludingitinthemajorityofpatientsthat are suspected of, but do not have the disease, is challenging. In recent years, much attention has been given to the role of clinical decision rules to objectively assess clinical probability, and several rules have been designed and validated15. The
usefulnessofclinicalassessmentincombinationwithaDdimertest,hasbeenshown in several management studies. In the 2040% of patients with a low clinical probability score in combination with a normal Ddimer result the diagnosis can be safely ruled out and no further diagnostic workup for PE is necessary69. The Wells
rule, introduced in 2000, is composed of seven variables obtained from medical history and physical examination (Table 1)4. It has gained popularity in Europe and
North America and has been implemented in several guidelines for the diagnostic workup of patients with suspected pulmonary embolism. The Wells rule assigns different points to the variables, which renders the calculation of a patient’s individualscoresomewhatcumbersome.RecentlyasimplerversionoftheWellsrule wasproposed,byassigningthesameweight(onepoint)toeachofthesevenvariables intheWellsrule(Table1)10.Inthisderivationset,the‘simplified’Wellsruleshowed
a similar diagnostic accuracy and clinical utility compared to the ‘original’ Wells rule10. The goal of the present study is to validate this simplified Wells rule in a
anothercohortofpatients11.
M
ETHODS
Forthepresentanalysisdatafromaprospectivemanagementstudywereused11.This
studyvalidatedadiagnosticstrategyforsuspectedPE,basedonclinicalprobability, DDimertest,compressionultrasonographyandhelicalcomputedtomography(CT). The study was performed in three teaching hospitals in Geneva and Lausanne, Switzerland and Angers, France. It was approved by the Ethics Committee of the Department of Medicine, Geneva University Hospital; the Ethics Committee of the Lausanne Medical School; and the Comité consultative de Protection des Personnes
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Table 1. Wells score – original and simplified.
Points ‘original’ Wells Points ‘simple’ Wells Clinical signs of DVT 3 1
Heart rate > 100/min 1.5 1 Recent surgery or immobilization 1.5 1 Previous PE or DVT 1.5 1
Hemoptysis 1 1
Malignancy 1 1
Alternative diagnosis less likely than PE 3 1 Cut-off for PE unlikely 4 1 PE = pulmonary embolism; DVT = deep venous thrombosis.
Adapted from: Wells et al.4 and Gibson et al .10
dans la Recherche Biomédicale des Pays de la Loire in Angers. All patients gave writteninformedconsentfortheirparticipationinthestudy.
Patients and management
Consecutive outpatients presenting to the emergency department with a clinical suspicion of acute pulmonary embolism were included between October 2000 and June 2002. Predefined exclusion criteria were: ongoing anticoagulant treatment for reasons other than venous thromboembolism; contraindication to CT scan (known allergy to iodine contrast agents or at risk of allergic reaction); creatinine clearance below 30 mL/min as calculated by the Cockcroft formula; informed consent impossible due to cognitive impairment; patient refusal; suspected massive pulmonaryembolismwithshock;pregnancy;estimatedsurvivallessthan3months; and followup not possible. The results of this diagnostic workup have been published previously11. Briefly, the study design was as follows: clinical probability
was assessed in all patients using the Geneva score3, with an option to override by
implicit assessment in case of a physician’s disagreement with the score. The seven itemsrequiredtocompute theWellsrulewerealsocollected,allowingretrospective calculation of this score. After assessing the clinical probability, a DDimer test was performed (enzymelinked immunosorbent assay (ELISA), Vidas Ddimer; Biomérieux,Marcyl’Etoile,France).Pulmonaryembolismwasconsideredruledoutif the Ddimer level was below 500 g/L. These patients were not treated with anticoagulants and followed up. Those with an abnormal DDimer level underwent
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proximal lowerlimb venous compression ultrasonography (CUS), and were treated withanticoagulantsifCUSdisclosedaproximaldeepvenousthrombosis.Allpatients withanormalCUSproceededtohelicalCT.PatientswithaninconclusiveCTorthose with a normal CT but a high clinical probability underwent further testing (pulmonaryangiographyorventilationperfusionlungscan).Patientswerefollowed by their family physicians and received a telephoneinterview by one of the study coordinatorsattheendofthe3monthfollowupperiod.
Validation of original and simplified Wells scores
Inthisanalysis,wecalculatedtheproportionofpatientsattributedtotwoprobability categories;“PEunlikely”and“PElikely”,andtheprevalenceofpulmonaryembolism percategory,usingboththeoriginalandthesimplifiedWellsrule.Thecutoffsforthe “PEunlikely”categorywereascoreof4pointsorlessfortheoriginalWellsrule4,and
a score of one point or less using the simplified Wells rule10. To gain further insight
intothedistributionofpatientscategorizedbythesimplifiedWellsrule,weelectedto calculate the prevalence of PE in two subcategories within the likely probability category.Inthelikelyprobabilitycategory,weselectedascoreoftwotorepresentan “intermediate”probability,andascoreof3to5tocorrespondtoa“high”probability. The unlikely probability category then corresponds to a “low” probability. The cut offs were chosen to create a reasonable trichotomous distribution similar to the original (trichotomous) Wells rule. To compare the different scores for safety and utility, we assessed the prevalence of PE in the low probability groups (low prevalenceendorsingsafety)during3monthsoffollowupandthesizeoftheselow probability groups (large groups endorsing clinical utility). Because clinical decision rulesaremostoftenusedtogetherwiththeresultofaDdimertest,theproportionof patients with a low clinical probability together with a normal Ddimer test result weredeterminedtocalculatetheproportionofpatientsinwhomfurthertestscould besafelywithheld.
Statistical analysis
For each score, 1) the proportion of patients classified in each clinical probability group,2)theprevalenceofPEineachgroup,and3)thethreemonththromboembolic risk in patients left untreated on the basis of the combination of clinical probability assessmentandresultsoftheDdimertest,wereestimatedwiththeir95%confidence intervals(CI).
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Table 2. Distribution of patients in the unlikely and likely clinical probability category of the two
decision rules and corresponding prevalence of pulmonary embolism. Proportion of patients in total;
% (95% CI) [n]
Prevalence of pulmonary embolism; % (95% CI) [n] Decision rule
Unlikely Likely Unlikely Likely Original Wells rule 78% (76-81%)
[722/922] 22% (19-25%) [200/922] 13% (11-16%) [95/722] 56% (49-63%) [112/200] Simplified Wells rule 70% (67-73%)
[644/922] 30% (27-33%) [278/922] 12% (9.7-15%) [77/644] 47% (41-53%) [130/278] Clinicalcharacteristicsofstudypatientswithorwithoutallrequireddatatocompute the Wells rule were compared using a chi2 test for qualitative variables, and a Studentttestforcontinuousvariables.
R
ESULTS
Patient characteristics
Atotalof965consecutiveoutpatientswithclinicalsuspicionofPEwereincludedin thestudy.Inthiscohort,theoverallprevalenceofPEatthetimeofinitialpresentation was23%(n=222)In43ofthe965patientsdataonthevariablesoftheWellsrulewere missing(themostfrequentlymissingvariablewas‘alternativediagnosislesslikely’), leaving922(96%)analyzablepatientsforthepresentanalysis.Thepatientsinwhom theWellsrulecouldnotbecalculatedhadaslightlyhigherrateofconfirmedPE(35% (15/43)vs.23%(207/922)p=0.06),lesspatientscomplainedofchestpain(54%(23/43) vs. 71% (658/922) p = 0.01), and there were more symptoms of deep venous thrombosis(DVT,33%(14/43)vs.20%(183/922)p=0.04).Thegroupswereotherwise comparable. In the original cohort, patients with a normal DDimer test (n=268) did notreceivefurtherinvestigationsandnoneofthemexperiencedVTEduringthethree monthsfollowup(0.0%,95%CI0.01.4%).Group size and prevalence of pulmonary embolism
TheoriginalWellsruleidentifiedaslightlylargerproportionofpatientsas‘unlikely’ comparedtothesimplifiedWellsrule:722(78%,95%CI7681%)and644(70%,95% CI6773%)respectively(Table2).
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Table 3. Distribution of patients per decision rule in three categories and corresponding
prevalence of pulmonary embolism.
Proportion of patients in total % (95%CI) [N]
Prevalence of pulmonary embolism % (95% CI) [N]
Decision rule
Low Intermediate High Low Intermediate High Original Wells rule 62% (59-65%) [571/922] 35% (32-38%) [325/922] 2.8% (1.9-4.1%) [26/922] 10% (7.9-13%) [58/571] 40% (35-45%) [129/325] 77% (58-89%) [20/26] Simplified Wells rule 70% (67-73%) [644/922] 20% (18-23%) [189/922] 9.7% (7.9-12%) [89/922] 12% (9.7-15%) [77/644] 40% (33-47%) [75/189] 62% (51-71%) [20/89] Original Wells rule: low, 0-2; intermediate, 2-6; high, > 6
Simplified Wells rule: low, 0-1; intermediate, 2; high 3-5
Theprevalenceofpulmonaryembolismperclinicalprobabilitycategoryisdetailedin Tables2and3.TheprevalenceofPEintheunlikelycategories(Table2)iscomparable for the two rules (13% and 12%, respectively). Using three levels of clinical probability,theprevalenceofPEwasalsocomparableineachprobabilitycategoryfor theoriginalandthesimplifiedWellsrule.
Safety and clinical utility of the clinical decision rules combined with D-dimer testing.
BecausenoneofthepatientswithanormalDdimerresultsufferedfromVTEduring followup in the original cohort, the incidence of VTE in patients with an unlikely probabilityforpulmonaryembolismincombinationwithanormalDdimerwas0%, similar for both scores (Table 4). The clinical utility of the scores, expressed as the proportion of patients in whom further tests could be safely withheld using the clinicaldecisionruleandDdimertestiscomparableforbothscores(Table4).
Table 4. Safety and clinical utility of the different scoring options of the clinical decision rules
combined with D-dimer testing.
Strategy Incidence of VTE during 3 months follow-up
Proportion of patients in whom further tests could be withheld n %, 95% CI %, 95% CI
Original Wells rule d4
and normal D-dimer 0/246 0.0% (0.0-1.5%) 28% (95% CI 25-31%) Simplified Wells rule d1
and normal D-dimer 0/234 0.0% (0.0-1.6%) 26% (95% CI 24-29%) VTE = venous thromboembolism.
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D
ISCUSSION
In this analysis, the original Wells rule and the simplified Wells rule display similar diagnostic accuracy and clinical utility. Compared to the results obtained in the derivationstudyofthesimplifiedrule,theincidenceofVTEinpatientscategorizedas “PEunlikely”andanormalDdimerresultissimilar(0.5%inthederivationstudy10
vs. 0.0% in this analysis), while the proportion of patients with such a combination wasslightlylower(26%comparedto30%inthederivationstudy10).Bothfiguresare
comparabletotheresultsobtainedwhenusingtheoriginalWellsrule.Inthepresent study, the prevalence of PE in the unlikely clinical probability category was similar using the simplified Wells rule compared with the original Wells rule. Also, the clinical utility of the simplified rule, reflected by the proportion of patients not requiring further testing based on clinical assessment and Ddimer result, was roughlysimilartothatoftheoriginalandmorecomplicatedWellsrule.
Asthisanalysiswasperformedinamulticentercohortcompletelydistinctfromthat whichservedtoderivethesimplifiedonepointWellsrule,webelievethatourresults provide additional validity to this rule, which could be easier to compute by busy clinicians.Indeed,itappearsthatassigningthesameweighttoeachvariabledidnot reduce predictive accuracy. Also, simplifying the dichotomized Wells rule did not reduceitsclinicalutility,astheproportionofpatientsinwhomfurthertestingcould be avoided using Ddimer testing and the simplified rule is not significantly lower thanthatobtainedbytheoriginalclassification(Table4).
The distribution of patients from this study cohort in a low, intermediate and high category bytheoriginalWellsrule andthecorrespondingprevalenceofPEineach categoryhavebeenpreviouslypublished12.Also,thetrichotomousoriginalWellsrule
and the Geneva score have been previously compared in a subset of the study sample13. The distribution of patients in the various categories in these previous
studiesiscomparabletoourresultsusingatrichotomousdistributionoftheoriginal Wellsrule.WealsocalculatedtheprevalenceofPEinthreeprobabilitycategoriesby the simplified Wells rule. This was done in order to get a better insight in the distributionofpatientsinthelikelycategoryofthesimplifiedrule andtobeableto compare this rule to existing trichotomous scores. The results obtained when using the simplified Wells rule in this study is comparable to results obtained using the Geneva score11 with similar predictive accuracies (prevalence of PE in the ‘low’,
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‘intermediate’,‘high’probabilitygroupsof12%,40%,62%and7%,34%,85%forthe simplified Wells rule and Geneva score, respectively) and is also comparable to the recently published revised Geneva score5 (prevalence of PE: 9.0%, 28%, 72% in the
‘low’,‘intermediate’and‘high’probabilitycategories,respectively).However,itwas not the aim of this study to derive a trichotomous score, these results are merely showntoclarifythedistributionofpatientswithinthelikelyprobabilitycategory.The highprevalenceofPE(40%)intheintermediatecategoryofthesimplifiedWellsrule supportsacutoffpointof1for“unlikely”and“likely”probabilitycategories.
There are several aspects of this study that require comment. First, the Wells rule (bothoriginalandsimplified)wascomputedretrospectivelyinthispatientcohort,in which another rule, the Geneva score, was used to guide patient management. Although all the information necessary to compute the Wells rule was acquired prospectively before any test was performed, there were 43 patients in whom the Wellsrulecouldnotbecalculated.ThesepatientshadaslightlyhigherrateofPEand associated DVT, and “alternative diagnosis less likely” was the most frequently missing variable. It is conceivable that the suspicion of PE was higher in these 43 patients.Becauseitisonlyalimitedproportionoftheentirecohortandthesepatients wereleftoutoftheanalysisforbothrules,theinterferenceinthecomparisonamong therulesisonlylimited.
In this cohort, none of the patients with a normal Ddimer test result suffered from VTEduringfollowup.Asaresultthisassayhadanegativepredictivevalueof100% forexcludingclinicallysignificantPE.Thismightseemoptimisticconsideringthefact thatthereareseveralstudiesthatindicatedthatitwasnotsafetomanagepatientson the Ddimer test result alone; in patients in whom PE is likely further diagnostic testing is usually advocated1417. However, the observed negative predictive value of
100% has no impact on our analysis, since this uncertainty is reflected by the 95% confidence interval of the 3month thromboembolic risk. This confidence interval is narrow, and a lower negative predictive value using another or the same Ddimer assaywouldhavethesameinfluencewhetherusingtheoriginalorthesimplifiedone point Wells rule. Finally, it is currently advised that exclusion of PE in patients is based on the outcome of a clinical decision rule in combination with a Ddimer test result.
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Inconclusion,inthisexternalvalidation,thesimplifiedWellsruleappearstohavethe same predictive accuracy as the original rule and a similar clinical utility. Also, it appears safe to rule out PE in combination with Ddimer measurement. The straightforwardness of the rule may enhance applicability. Therefore, the simplified onepointWellsrulecouldbeagoodalternativetomorecomplicatedrules,although prospectivevalidationiswarranted.
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EFERENCELIST
1. Kline JA, Nelson RD, Jackson RE, Courtney DM. Criteria for the safe use of D-dimer testing in emergency department patients with suspected pulmonary embolism: a multicenter US study. Ann Emerg Med. 2002;39:144-152.
2. Miniati M, Prediletto R, Formichi B et al. Accuracy of clinical assessment in the diagnosis of pulmonary embolism. Am J Respir Crit Care Med. 1999;159:864-871.
3. Wicki J, Perneger TV, Junod AF, Bounameaux H, Perrier A. Assessing clinical probability of pulmonary embolism in the emergency ward: a simple score. Arch Intern Med. 2001;161:92-97. 4. Wells PS, Anderson DR, Rodger M et al. Derivation of a simple clinical model to categorize
patients probability of pulmonary embolism: increasing the models utility with the SimpliRED D-dimer. Thromb Haemost. 2000;83:416-420.
5. Le Gal G, Righini M, Roy PM et al. Prediction of pulmonary embolism in the emergency department: the revised Geneva score. Ann Intern Med. 2006;144:165-171.
6. Wells PS, Anderson DR, Rodger M et al. Excluding pulmonary embolism at the bedside without diagnostic imaging: management of patients with suspected pulmonary embolism presenting to the emergency department by using a simple clinical model and d-dimer. Ann
Intern Med. 2001;135:98-107.
7. van Belle A, Buller HR, Huisman MV et al. Effectiveness of managing suspected pulmonary embolism using an algorithm combining clinical probability, D-dimer testing, and computed tomography. JAMA. 2006;295:172-179.
8. Ten Cate-Hoek AJ, Prins MH. Management studies using a combination of D-dimer test result and clinical probability to rule out venous thromboembolism: a systematic review. J
Thromb Haemost. 2005;3:2465-2470.
9. Perrier A, Roy PM, Sanchez O et al. Multidetector-row computed tomography in suspected pulmonary embolism. N Engl J Med. 2005;352:1760-1768.
10. Gibson NS, Sohne M, Kruip MJ et al. Further validation and simplification of the Wells clinical decision rule in pulmonary embolism. Thromb Haemost. 2008;99:229-234.
11. Perrier A, Roy PM, Aujesky D et al. Diagnosing pulmonary embolism in outpatients with clinical assessment, D-dimer measurement, venous ultrasound, and helical computed tomography: a multicenter management study. Am J Med. 2004;116:291-299.
12. Righini M, Le GG, Perrier A, Bounameaux H. Clinical probability assessment of pulmonary embolism by the Wells' score: is the easiest the best? J Thromb Haemost. 2006;4:702-704. 13. Chagnon I, Bounameaux H, Aujesky D et al. Comparison of two clinical prediction rules and
implicit assessment among patients with suspected pulmonary embolism. Am J Med. 2002;113:269-275.
14. Kelly J, Hunt BJ. A clinical probability assessment and D-dimer measurement should be the initial step in the investigation of suspected venous thromboembolism. Chest. 2003;124:1116-1119.
15. Ginsberg JS, Wells PS, Kearon C et al. Sensitivity and specificity of a rapid whole-blood assay for D-dimer in the diagnosis of pulmonary embolism. Ann Intern Med. 1998;129:1006-1011. 16. Di Nisio M, Squizzato A, Rutjes AW, Buller HR, Zwinderman AH, Bossuyt PM. Diagnostic
accuracy of D-dimer test for exclusion of venous thromboembolism: a systematic review. J
Thromb Haemost. 2007;5:296-304.
17. Gibson N.S, Sohne M, Gerdes VE, Nijkeuter M, Buller HR. The importance of clinical probability assessment in interpreting a normal D-dimer in patients with suspected pulmonary embolism. Chest. 2008; in press.
