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A new rapid bedside assay for d-dimer measurement (Simplify d-dimer) in the diagnostic work-up for deep vein thrombosis

2003; Elsevier BV; Volume: 1; Issue: 12 Linguagem: Inglês

10.1111/j.1538-7836.2003.0543d.x

1538-7933

Michela Cini, Cristina Legnani, K. Cavallaroni, F. Bettini, G Palareti,

Central Venous Catheters and Hemodialysis

Dear Sir, The measurement of d-dimer levels is of clinical benefit in the diagnostic work-up for the exclusion of deep vein thrombosis (DVT), especially in symptomatic outpatients [1Wells P.S. Hirsh J. Anderson D.R. Lensing A.W.A. Foster G. Kearon C. Weitz J. Dovidio R. Cogo A. Prandoni P. Girolami A. Ginsberg J.S. Accuracy of clinical assessment of deep-vein thrombosis.Lancet. 1995; 345: 1326-30Abstract PubMed Scopus (651) Google Scholar]. Several assays for the measurement of plasma d-dimer levels are now commercially available. However, the SimpliRed d-dimer assay (Agen Biomedical Limited, Brisbane, QLD, Australia) has until recently been the only rapid and qualitative method that can be used in emergencies without any laboratory equipment [2Wells P.S. Brill-Edwards P. Stevens P. Panju A. Patel A. Douketis J. Massicotte M.P. Hirsh J. Weitz J.I. Kearon C. Ginsberg J.S. A novel and rapid whole-blood assay for d-dimer in patients with clinically suspected deep vein thrombosis.Circulation. 1995; 91: 2184-7Crossref PubMed Scopus (229) Google Scholar]. This method is easy, can be performed at the bedside, and provides within a few minutes a qualitative result based upon the presence or absence of agglutination on a test plate. However, the extent of agglutination is directly related to the concentration of d-dimer in the blood sample and is not always clearly discernible, thus the detection of agglutination may differ between different observers. Results obtained with the SimpliRED are, in fact, variable [2Wells P.S. Brill-Edwards P. Stevens P. Panju A. Patel A. Douketis J. Massicotte M.P. Hirsh J. Weitz J.I. Kearon C. Ginsberg J.S. A novel and rapid whole-blood assay for d-dimer in patients with clinically suspected deep vein thrombosis.Circulation. 1995; 91: 2184-7Crossref PubMed Scopus (229) Google Scholar, 3Ginsberg J.S. Wells P.S. Brill-Edwards P. Donovan D. Panju A. Van Beek E.J.R. Patel A. Application of a novel and rapid whole blood assay for d-dimer in patients with clinically suspected pulmonary embolism.Thromb Haemost. 1995; 73: 35-8Crossref PubMed Scopus (121) Google Scholar, 4Turkstra F. Van Beek E.J.R. Ten Cate J.W. Büller H.R. Reliable rapid blood test for the exclusion of venous thromboembolism in symptomatic outpatients.Thromb Haemost. 1996; 76: 9-11Crossref PubMed Scopus (116) Google Scholar, 5Fiessinger J.N. Héron E. Jacq F. Rance A. Emmerich J. Rapid blood test for the exclusion of venous thromboembolism in symptomatic outpatients.Thromb Haemost. 1997; 77: 1042-3Crossref PubMed Scopus (12) Google Scholar, 6Jacq F. Héron E. Rance A. Césarini M. Emmerich J. Fiessinger J.N. Evaluation of a rapid blood test for the exclusion of venous thromboembolism in symptomatic outpatients.Presse Med. 1997; 26: 1132-4PubMed Google Scholar, 7Reber G. De Moerloose P. Coquoz C. Bounameaux H. Comparison of two rapid d-dimer assays for the exclusion of venous thromboembolism.Blood Coag Fibrinol. 1998; 9: 387-8Crossref PubMed Scopus (19) Google Scholar, 8Wildberger J.E. Vorwerk D. Kilbinger M. Piroth W. Hunter D.W. Wienert V. Günther R.W. Bedside testing (SimpliRED) in the diagnosis of deep vein thrombosis. Evaluation of 250 patients.Invest Radiol. 1998; 33: 232-5Crossref PubMed Scopus (23) Google Scholar, 9Van Der Graaf F. Van Den Borne H. Van Der Kolk M. De Wild P.J. Janssen G.W.T. Van Uum S.H.M. Exclusion of deep venous thrombosis with d-dimerimer testing – comparison of 13 d-dimer methods in 99 outpatients suspected of deep venous thrombosis using venography as reference standard.Thromb Haemost. 2000; 83: 191-8Crossref PubMed Scopus (212) Google Scholar]; the sensitivity and the negative predictive value have been reported as ranging between 40 and 100%. Moreover, some authors have noted a high interobserver variability (2.4–8% discordant readings, with kappa coefficient (κ) values ranging between 0.47 and 0.95) [7Reber G. De Moerloose P. Coquoz C. Bounameaux H. Comparison of two rapid d-dimer assays for the exclusion of venous thromboembolism.Blood Coag Fibrinol. 1998; 9: 387-8Crossref PubMed Scopus (19) Google Scholar, 10Turkstra F. Van Beek E.J.R. Büller H.R. Observer and biological variation of a rapid whole blood d-dimer test.Thromb Haemost. 1998; 79: 91-3Crossref PubMed Scopus (39) Google Scholar, 11De Monyé W. Huisman M.V. Pattynama P.M.T. Observer dependency of the SimpliRed d-dimer assay in 81 consecutive patients with suspected pulmonary embolism.Thromb Res. 1999; 96: 293-8Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar]. The aim of this study was to evaluate the diagnostic accuracy of a new rapid, bedside assay for qualitative testing of d-dimer in whole blood, the Simplify d-dimer (Agen Biomedical Limited), in outpatients with clinically suspected DVT. Similar to SimpliRed, this assay is also easily performed, is suitable for emergencies, and provides results within 10 min after the application of the sample, without the use of specific instruments. The Simplify d-dimer assay is an immunochromatography test performed on whole blood or plasma and based on two d-dimer-specific antibodies: a murine monoclonal antibody, DD3B6/22, specific for d-dimer conjugated to colloidal gold particles, and a second d-dimer-specific murine monoclonal antibody. The antibody–gold conjugate binds specifically to d-dimer-containing molecules in the patient sample to form a complex that migrates through a membrane in the aqueous phase until it is captured and concentrated on a zone to which the second d-dimer-specific murine monoclonal antibody has been bound. The concentration of the complexes in this area (test zone) causes a pink/purple line to appear on the membrane. Uncaptured gold conjugate continues to flow towards the end of the strip where it is bound to the procedural control zone by a sheep antimurine IgG antibody. Formation of a pink/purple PC line indicates the device is working as designed. The study included 120 consecutive outpatients (52 men; mean age 64 years, range 20–96 years) referred to our outpatient clinic for suspected DVT of a lower limb. The exclusion criteria were the following: previous episode of DVT, stable symptoms lasting more than 15 days, therapeutic or prophylactic anticoagulant treatments already underway at presentation, pregnancy. The Vidas d-dimer test (BioMèrieux, Marcy l'Etoile, France) was used as the reference test for d-dimer measurement; the cut-off value was 500 ng mL−1. The approval of the local ethics committee was obtained, as was the patient's consent to follow the diagnostic work-up adopted in our outpatient clinic. Blood was sampled from the patients at presentation and tested by technicians unaware of the patient's clinical diagnosis. Blood was drawn from a forearm vein by clean venipuncture and anticoagulated by trisodium citrate (0.129 mol L−1). Patients were classified as DVT positive or negative according to the results of objective testing and a 3-month follow-up. The DVT diagnostic work-up used in our institution is based on: pretest clinical probability, according to the score proposed by Wells et al. [12Wells P.S. Anderson D.R. Bormanis J. Guy F. Mitchell M. Gray L. Clement C. Robinson K.S. Lewandowski B. Value of assessment of pre-test probability of deep-vein thrombosis in clinical management.Lancet. 1997; 350: 1795-8Abstract Full Text Full Text PDF PubMed Scopus (987) Google Scholar]; d-dimer measurement (Vidas d-dimer); compression ultrasound (CUS), according to standard criteria [13Lensing A.W.A. Prandoni P. Brandjes D. Huisman P.M. Vigo M. Tomasella G. Krekt J. Ten Cate J.W. Huisman M.V. Büller H.R. Detection of deep-vein thrombosis by real-time B-mode ultrasonography.N Engl J Med. 1989; 320: 342-5Crossref PubMed Scopus (813) Google Scholar], to assess proximal DVT. The CUS test is repeated after 5–7 days in patients with a negative initial CUS examination and high/moderate pretest clinical probability or positive d-dimer test (>500 ng mL−1). Patients were considered DVT positive if one of the following occurred: (i) absence of compressibility of the common femoral and/or popliteal veins on CUS at presentation or 5–7 days after; or (ii) symptomatic venous thromboembolic event, verified by objective testing within 3 months after presentation. Patients were considered DVT negative when one of the following results occurred along with the absence of symptomatic venous thromboembolic event within 3 months of follow-up: (i) normal initial CUS results in the presence of low pretest clinical probability and negative VIDAS D-Dimer test (<500 ng mL−1); or (ii) normal serial CUS results. Thirty-five patients (29.2%) were classified as DVT positive. Twenty patients with negative initial CUS examination and high/moderate pretest clinical probability and/or positive Vidas d-dimer test where examined after 5–7 days by CUS testing; no DVT was detected. In 17 patients, superficial phlebitis was diagnosed. Symptomatic venous thromboembolism did not occur in any of the remaining 48 patients during the 3-month follow-up period. To evaluate the interobserver variability, one strip was inspected at the same time by two observers; both independently recorded their interpretation of the test outcome and the results were compared afterwards. The interobserver variability was evaluated in 30 patients using the kappa coefficient (κ) [14Altman D.G. Practical Statistics for Medical Research. Chapman & Hall, 1991Google Scholar]. As reported in Table 1, the two observers disagreed in 1 case (3.3%), for a κ-value of 0.92 (95% confidence interval 0.77–1.00, P < 0.01). The interobserver agreement was very good according to the interpretation of κ-values by Altman [14Altman D.G. Practical Statistics for Medical Research. Chapman & Hall, 1991Google Scholar].Table 1Analysis of interobserver variability of the Simplify d-dimer assay and agreement between the Simplify and the VIDAS d-dimer assayFirst observerPositiveNegativeTotalSecond observer Positive909 Negative12021 Total102030κ = 0.92 (95% confidence interval 0.77–1.00), P < 0.01, agreement 29/30 = 96.7%Simplify d-dimerPositiveNegativeTotalVIDAS d-dimer >500 ng mL−171980 ≤500 ng mL−133740 Total7446120κ = 0.78 (95% confidence interval 0.67–0.90), P < 0.01, agreement 108/120 = 90%AssaySensitivitySpecificityNPVPPVSimplify d-dimer*Data are presented as percentage (95% confidence interval). NPV = negative predictive value; PPV = positive predictive value.100.0%52.9%100.0%46.7%(90.0–100.0)(41.8–63.8)(92.1–100.0)(35.1–58.5)VIDAS d-dimer*Data are presented as percentage (95% confidence interval). NPV = negative predictive value; PPV = positive predictive value.†A cut-off value of 500 ng mL−1 was used for VIDAS d-dimer.100.0%48.8%100.0%47.5%(90.7–100.0)(37.6–60.1)(91.2–100.0)(36.2–59.0)* Data are presented as percentage (95% confidence interval). NPV = negative predictive value; PPV = positive predictive value.† A cut-off value of 500 ng mL−1 was used for VIDAS d-dimer. Open table in a new tab The concordance between the Simplify and VIDAS d-dimer assays to classify a given patient as having a positive or a negative result was estimated using κ values. A good concordance was found (κ = 0.78, 95% confidence interval 0.67–0.90, P < 0.01). The agreement between the two assays was 90% (Table 1). Sensitivity, specificity, positive and negative predictive values of the two methods were calculated using standard methods. The sensitivity and negative predictive value were 100% for both tests (Table 1). The corresponding specificity and positive predictive value were similar (specificity: 52.9% and 48.8%; positive predictive value: 46.7%, and 47.5% for the Simplify and VIDAS tests respectively). In conclusion, the Simplify d-dimer test proved to have high sensitivity and good specificity, with minimal false-negative and -positive results when used for the DVT diagnostic work-up in outpatients. The test produced results fully comparable to those obtained with a well-established method (VIDAS d-dimer). In comparison with the SimpliRed assay, the Simplify test seems to have a lower interobserver variability, probably due to a clearer display of positive/negative results. This characteristic may help the bedside use of this assay even if performed by inexperienced operators. For these reasons, this assay seems to have great clinical potential, although its place in the diagnostic strategy of DVT remains to be determined in prospective management studies.