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2 Thromboss and Haemostass F. K. Schattauer Verlagsgesellschaft mbh (Stuttgart) 77 (2) (1997) Relablty of Fve Rapd D-Dmer Assays Compared to ELISA n the Excluson of Deep Venous Thromboss 9 M. C. H. Janssen1, A. E. Heebels2, M. de Metz3, H. Verbruggen4, H. Wollershem1, S. Janssen2, M. M. J, Schuurmans2,1. R. O. Nováková5 From the Department of Medcne, Dvsons of General Interna Medcne, 5Hematology and 4Centra Hematologcal Laboratory, Unversty Hosptal, Njmegen, the Departments of nternal Medcne and 3Central ncal Chemcal Laboratory, Cansus Whelmna Hosptal, Njmegen, The Netherlands Summary decades (4, 5). None of these has been able to acheve the absolute Studes measurng the fbrn degradaton product D-Dmer (DD) usng enzyme-lnked mmunosorbent assays (ELISA) n patents wth venographcally proven deep venous thromboss (DVT) suggest that t s possble to exclude DVT when DD level s below a certan cut-off level However, ELISA methods are tme-consumng and not avalable n all laboratores. Dfferent rapd latex-agglutnaton assays have been nvestgated, but ther senstvty s consderably lower. In the present study we compared the value of four novel latex DD tests (Tnaquant, Mnutex, Ortho and SmplRed ) and one rapd ELISA (VIDAS ) to a classcal ELISA DD assay (Organon Mab Y18 ) n 132 patents suspected of DVT. The VIDAS, a new quanttatve automated ELISA, had a senstvty of 100% and a negatve predctve value of 100% for both proxmal and dstal DVT at a cut-off level of 500 ng/ml. The Tnaquant assay, a new quanttatve latex method, had a senstvty of 99% and a negatve predctve value of 93% for both proxmal and dstal DVT at a cut-off level of 500 ng/ml. For proxmal DVT only, both assays had a senstv-» ty and negatve predctve value of 100%. VIDAS and Tnaquant correlated well wth ELISA (correlaton of r = 0.96 and r = 0.98 respectvely). Senstvtes of the sem-quanttatve latex assays Mnutex, Ortho and SmplRed were consderably lower (77%, 51% and 61% respectvely). These results suggest that VIDAS and Tnaquant may be used nstead of ELISA DD n the excluson of DVT. Tnaquant can be performed wthn 20 mn and VIDAS wthn 35 mn. Both assays mght be used as a routne screenng test and should be evaluated n large clncal management studes. degree of anatomcal defnton that s possble wth contrast venography, but some of these tests have a dagnostc threshold that permts safe clncal management. Seral use of ultrasonography has recently been shown to be a safe method of managng outpatents who are suspected of havng lower lmb DVT (6). However, a smple and relable blood test that could exclude DVT would have practcal and economc advantages. Increased levels of plasma D-Dmer (DD) - a cross-lnked fbrn degradaton product reflectng fbrn formaton and subsequent dssoluton - measured by enzyme-lnked mmunosorbent assay (ELISA), have been reported n patents wth proven DVT by venography (7-10). One of the major problems of blood tests for DVT s the lack of specfcty of the markers. Elevated levels of DD are also found n a wde varety of other clncal condtons (e. g. myocardal nfarcton, nflammaton, malgnancy and lver dsease) (11). As a consequence * studes measurng DD n patents wth venographcally proven DVT suggest that t should only be possble to exclude ths condton. A seres of dfferent assays have been evaluated for the presence or absence of DVT. ELISA assays have been proven to be senstve enough, but ths technque s rather tme-consumng (t takes about 2 h) and not suted for routne measurements and thus has lttle clncal utlty as a routne screenng test (7,12). DD latex agglutnaton assays are performed more rapdly, but ther senstvty s consderably lower (9, 10,13-19). Recently DD latex assays have reganed nterest as an emergency dagnostc, because newly avalable assays dsplay hgher senstvty. In the present study the value of fve novel, rapd DD assays n the excluson of DVT n outpatents wth suspected DVT was assessed and compared to ELISA. Introducton In order to prevent the morbdty and mortalty assocated wth untreated deep venous thromboss (DVT) a relable dagnoss and therapy s requred. The clncal dagnoss of DVT s unsatsfactory. Over 50% of patents wth symptoms suggestng DVT do not have thromboss (1-3). The defntve test for the dagnoss of DVT s stll classcal ascendng venography. Because ths technque s nvasve several nol-nvasve tests have been developed over the past three Patents and Methods Patents In two clncal centers (Unversty Hosptal Njmegen and Cansus Whelmna Hosptal) patents referred to the outpatents department or emergency unt because of clncally suspected DVT were enrolled n the study after gvng nformed consent. Only ambulant outpatents were ncluded. No other excluson crtera were appled. At the tme of ncluson age, gender, duraton of symptoms and rsk factors (mmoblzaton, prevous DVT, surgery, malgnancy, pregnancy, oral contraceptves) were recorded. Vascular Testng Correspondence to; Dr. M. C. H, Janssen, Department of Medcne, Dvson of General Internal Medcne, Unversty Hosptal Njmegen, PO Box 9101, 6500 HB Njmegen, The Netherlands - Tel: ; FAX Number; After blood was drawn patents were submtted to compresson ultrasound (C-US) of the affected extremty. The deep venous system from the poplteal to the lac ven was examned (4, 20, 21). Lack of full compressblty was the sole crtera for DVT. In case of a postve result, patents were admnstered for 262

3 Table 2 Senstvty and negatve predctve values of the dfferent assays for proxmal DVT Assay sens overall sens prox NPV overall NPV prox (* ) (%) (%) (%) ELISA (500 ng/ml) VIDAS (500 ng/ml) Tnaquant (500 ng/ml) Smplred Mnutex Ortho false postve fracton (%) Fg. ] ROC curve analyss of the accuracy of Tnaquant plasma concentratons for DVT detected by compresson ultrasound or venography, D-Dmer values (ng/ml) correspondng to senstvtes of 49%, 60%, 75%, 89% and 99% are shown sens senstvty NPV = negatve predctve value overall = proxmal + dstal prox proxmal Table 1 Senstvty, specfcty, postve predctve value and negatve predctve value of the dfferent DD-assays Assay sens (%) spec (%) NPV (%) PPV {%) Duraton of the test (mnutes) ELISA (500 ng/ml) VIDAS (500 ng/ml) Tnaquant (500 ng/ml) SmplRed Mnutex Ortho sens = senstvty spec specfcty NPV = negatve predctve value PPV = postve predctve value = 95% confdence nterval standard antcoagulant therapy. Whenever the C-US was nconclusve, that means n case the deep vens could not be adequately vsualzed, venography was performed and regarded as the defntve test. Also each tme dstal DVT was suspected venography was performed. If negatve C-US results were obtaned, C-US was repeated between 3 and 7 days after the ntal testng f clncal symptoms of DVT perssted. Laboratoy Testng At the tme of ntal presentaton from all patents 4.5 ml of blood was drawn nto a vacutaner tube contanng 0.5 ml 3.8% sodum ctrate. Platelet poor plasma was prepared by centrfugaton at 4000 X g for 10 mn. Plasma was snap-frozen n alquots and stored at -70 C untl assayed. DD assays were performed usng commercally avalable kts. The results of the tests were not made known to the person performng the vascular testng and the results of the vascular testng were not known to the laboratory techncan. Because some of the assays are subject to nter-observer varablty each assay was performed at the same tme by the same laboratory techncan. The followng DD-assays were performed: (1) ELISA: Mah Y18 (Organon Teknka, Belgum) and (2) VIDAS (Boméreux, France), a quanttatve ELISA method automated on VIDAS mmunoanalyzer. Latex: (3) Ortho Dmertest (Ortho dagnostc systems Inc, Belgum), (4) Mnutex (Bopool, Sweden), (5) SmplRed (Agen dagnostcs lmted, Australa) and (6) Tnaquant (Boehrnger Mannhem, Germany). Ortho and Mnutex D-Dmer are sem-quanttatve assays; agglutnaton takng place n undluted plasma was regarded as a postve test. SmplRed s an autologous red cell agglutnaton assay. Ths assay can be performed mmedately n whole blood. For practcal reasons we centrfugated the blood and stored the plasma untl assayed. At the tme of the assay erythrocytes were added ( add-back procedure). Tnaquant s a new quanttatve latex assay. It was performed on a Htach 911 clncal chemstry analyzer. It has been standardzed before aganst the ELISA test Asserachrom D-Dmer and the correlaton between the two assays was (22). Analyss The presence or absence of DVT was determned on the bass of the vascular testng. The senstvty, specfcty and postve and negatve predctve values wth 95% confdence lmts () of each assay were calculated accordng to the presence of DVT on ultrasonography or venography usng two by two tables. For ELISA, VIDAS and Tnaquant Recever Operator Characterstcs (ROC) curves were constructed by plottng the senstvty (true postve fracton) versus 1-specfcty (false postve fracton) (23). Cut-off values were chosen based on optmal senstvty and negatve predctve value. Correlaton was calculated accordng to Spearman. Results «Durng the study perod (March-December 1995) 132 patents (83 females and 49 males) were enrolled. The mean age was 59 years (range 22 to 89 years). In 78 patents proxmal DVT was detected by C-US. In 26 patents venography was performed; n 11 patents dstal DVT was detected and n 15 patents venography was negatve. In 28 patents C-US was negatve. Only one patent wth an ntally negatve 263

4 VIDAS DD (ng/ml) Tnaquant (ng/ml) ELISA (ng/ml) ELISA (ng/ml) Fg. 2 Correlaton between the ELISA and VIDAS (r = 0.96) and Tnaquant assay (r = 0.98) VIDAS DD (ng/ml) C-US developed persstng symptoms and was found to have ven ncompressblty at follow-up. In summary proxmal DVT was detected n 59% and dstal DVT n 8% (overall prevalence 67%). Rsk factors for DVT were found n 66 patents (73%) n the group wth DVT (14 mmoblzaton, 20 malgnancy, 13 prevous DVT, 2 prevous surgery, 6 recent pregnancy, 11 oral antconceptves) and n 21 patents (50%) n the group wthout DVT (2 mmoblzaton, 3 malgnancy, 5 prevous DVT, 7 recent surgery, 4 oral antconceptves). The ROC curve of the accuracy of Tnaquant for all detected D VT s shown n Fg* 1. The ROC curve for ELISA and VIDAS was determned n the same way. For both assays senstvty and specfcty were optmal at a cut-off level of 500 ng/ml. Table 1 shows the overall senstvty, specfcty, postve and negatve predctve values of the dfferent assays. At a cut-off level of 500 ng/ml overall senstvtes for Tnaquant (ng/ml) no dstal pro xm a l D V T D V T D V T ELISA, VIDAS and Tnaquant were 98%, 100% and 99% respectvely. Negatve predctve values were 88%, 100% and 93% respectvely* The senstvtes of the three other latex tests were consderably lower (respectvely 61%, 77% and 51% for Smplred, Mnutex and Ortho ). Table 2 shows the senstvty and negatve predctve value for proxmal DVT only; senstvty and negatve predctve value for VIDAS and Tnaquant were both 100%. Fg. 2 shows that there was a good correlaton between ELISA and VIDAS (r = 0.96) and between ELISA and Tnaquant (r = 0.98), Fg. 3 shows the results of the VIDAS and Tnaquant tests for three categores of patents: (1) absence of DVT, presence of (2) dstal and (3) proxmal DVT, Values exceedng 10,000 ng/ml were exclusvely found n patents wth a proven DVT. Fg. 3 shows that the results of both assays are very smlar and that accordng to both assays n all patents wth DVT (except for one patent wth dstal DVT) the DD exceeded 500 ng/ml. DVT DVT DVT Fg. 3 Values of the VIDAS and Tnaquant assays n three dfferent groups of patents; no DVT, dstal DVT and proxmal DVT. All patents exceedng DD 10,000 ng/ml got the value 10,000 n the fgure. DVT = deep venous thromboss Dscusson The ratonale for performng ths study was to see f t was feasble to use a rapd screenng test to exclude the presence of DVT n outpatents. We excluded npatents because DD s elevated n many other 264

5 pathologcal/comorbd condtons (e. g. malgnancy, nfecton, myocardal nfarcton, lver dsease) (11). Most hosptals are usng non-nvasve tests to evaluate dagnoss of DVT. C-US has proven to be the most relable dagnostc test (6). Seral testng s necessary to detect ascendng dstal DVT. We compared the dagnostc effcacy of fve rapd DD assays wth classcal ELISA n clncally suspected DVT. The dagnoss of DVT was made by C-US. Venography, consdered as gold standard was not performed routnely. However, f C-US was nconclusve or f dstal DVT was suspected, venography was performed. If clncal symptoms perssted seral C-US was performed. In only one patent ven ncompressblty developed at follow-up. Because many patents wth symptoms suggestve of DVT appear not to have DVT by objectve testng (1,2), a smple screenng test to rule out DVT relably, would avod unnecessary further dagnostc procedures. Ideally such a test must have a hgh senstvty n order to rule out the dagnoss DVT correctly as these patents would be undertreated. reason of the dfferent results. Both alternatves of performng the Smplred assay should be compared to assure ths explanaton. The prevalence of DVT n our group of patents was relatvely hgh compared to other studes. In these studes prevalence vares between 30 and 50%. A reason for ths mght be the strct referral pattern of the general practtoners to our hosptal reflected n the relatvely hgh number of patents wth rsk factors for DVT, Another reason mght be that durng the nght hours we mssed some samples of patents wth a negatve C-US. In summary the VIDAS and Tnaquant assays used n ths study appeared to be sutable n the excluson of DVT. The problem of the other sem-quanttatve latex tests was nsuffcent senstvty. Although the tests have a hgh negatve predctve value (100%, %), the safety of wthholdng antcoagulant therapy n patents wth clncally suspected DVT and negatve DD needs confrmaton n a prospectve tral of a large number of consecutve outpatents. Based on these results management studes should be performed to examne the safety and cost-effects of ths approach. asscal ELISA assays have proven to be senstve (7, 12). The dsadvantage of ELISA tests s that they are tme-consumng and not sutable for routne measurement. In vew of the fact that ELISA tests last at least 120 mn and that latex agglutnaton methods are extremely smple and rapd to perform (5-20 mn), the avalablty of a relable Acknowledgement The study was supported by a grant from SWOIG (Stchtng Wetenschappeljk Onderzoek Interne Geneeskunde CWZ). latex test s most nterestng. The studes reported usng latex tests showed dscordant results (10, 12, 14). Senstvtes of most of the currently avalable latex assays are not suffcently hgh, except for the recently developed SmplRed assay (24); Wells et al. demonstrated a senstvty of 93% and a negatve predctve value of 98% for ths assay. More rapd ELISA and more senstve latex DD assays have been developed recently. We nvestgated the accuracy of a rapd ELISA (VIDAS ) and 4 latex assays (Tnaquant, Mnutex, Ortho and SmplRed ). The results of VIDAS and Tnaquant were equal to those of prevous reports about ELISA. We also found a good correlaton wth the classcal ELISA (r = 0.96 and r = 0.98 for VIDAS and Tnaquant respectvely). For VIDAS these results are comparable to former studes (25, 26). Both' assays have 100% senstvty ( %) and 100% negatve predctve value ( %) for proxmal DVT. The measurement of plasma DD n symptomatc patents wth clncally suspected DVT allows excluson of proxmal DVT when negatve (<500 ng/ml); the negatve predctve value of the test beng 100% ( %). The specfcty of VIDAS and Tnaquant was relatvely low (respectvely 19% and 33%). As t means that accordng Tnaquant one thrd of the patents wthout DVT could be sent home wthout further nvestgatons t may be concluded that t mght be a useful test as frst screenng n outpatents. The specfcty of VIDAS s lower than prevously reported (25, 26). In ths study only 8 out of 42 patents wthout DVT could have been sent home wthout further nvestgatons. Another dsadvantage of VIDAS s that ths ELISA can only be performed on a dedcated analyzer, whle Tnaquant can be performed on routne clncal chemstry analyzers such as the Htach, whch s used n ths study. The remanng three latex tests had a lower senstvty and negatve predctve value when compared to standard non-nvasve tests. These cannot be regarded as adequate. Ths lack of senstvty has been observed n other studes. The results of the SmplRed assay were dfferent from the senstvty and negatve predctve value reported by Wells et al. (24). However, they performed the DD assay mmedately n whole blood, whereas for practcal reasons we centrfugated the blood and stored the plasma untl assayed. At the tme of the assay erythrocytes were added ( add-back procedure). Ths mght be the References 1. Cranley II, Canos AJ, Sull WJ. The dagnoss of deep venous thromboss. Fallblty of clncal symptoms and sgns. Arch Surg 1976; 111: Barnes RW, Wu KK, Hoak JC. Fallblty of the clncal dagnoss of venous thromboss. JAMA 1975; 234: Koopman MM, van Beek EJ, ten Cate JW. Dagnoss of deep ven thromboss. Prog Cardovasc Ds 1994; 37: * Btller HR, Lensng AWA, Hrsh J, ten Cate JW. Deep ven thromboss: new non-nvasve dagnostc tests. Thromb Haemost 1991; 66: Cogo A, Lensng AWA, Wells P, Prandon P, Btller HR. Nonnvasve objectve tests for the dagnoss of clncally suspected deep-ven thromboss. Haemostass 1995; 25: Hejboer H, Bller HR, Lensng AW, Turpe AG, Colly LP, ten Cate JW. 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