SummaryThe performance of a new automated ELISA for a rapid, individual and quantitative measurement of plasma D-dimer (VIDAS D-dimer) has been evaluated. First, a study of 100 patients was performed in order to choose the best couple of antibodies in comparison with an already clinically validated ELISA. Then the results were certified in a prospective study including 195 consecutive patients suspected of pulmonary embolism (PE). For a cut-off level of 500 ng/ml VIDAS D-dimer showed a sensitivity of 100% (95% confidence interval 92-100), a specificity of 37.6%, a negative predictive value of 100% (95% CI 93.3-100) and a positive predictive value of 33.1%. During a 6 months’ follow-up no patient (95% CI 0-6.4) with D-dimer <500 ng/ml presented a new suspicion of venous thromboembolic disease. These results suggest that this rapid and single-dose ELISA provides a very useful tool for the clinician to exclude on a day-to-day basis the diagnosis of PE.

VIDAS D-dimer (bioMérieux) is a new quantitative ELISA for D-dimer determination designed for the VIDAS automated system. The test contains single-dose, ready-to-use reagents and is completed within 35 min. Quantitative results are obtained from a calibration curve stored in the software of the system and expressed as fibrinogen equivalent units. The two-step capture/tag test relies on two complementary monoclonal anti-D-dimer antibodies, the second one being labeled with alkaline phosphatase. The upper limit of the measuring range is 1000 micrograms/L and the lower detection limit is &lt;50 micrograms/L, which is below the lower limit of the reference interval (68-494 micrograms/L). Reproducibility (CV) within and between runs ranges from 5% to 7%. There is no interference from heparin, bilirubin, hemoglobin, fibrinogen degradation products, or plasma turbidity. Comparison with a conventional ELISA (y) gave good correlation (r= 0.91, n= 579) and comparable results (y= 1.35x - 148, S(y/x)= 750), especially for D-dimer concentrations ranging from 0 to 1000 micrograms/L (y= 1.09x - 10.6, r= 0.88, S(y/x)= 170).

SummaryActivated protein C reduces thrombin generation by inactivating factors V and VIII in the presence of protein S. This prompted us to develop an assay which would allow specific exploration of this reaction. The total amount of thrombin formed in plasma after activation by tissue factor and phospholipids was reduced by adding thrombomodulin. This addition allowed protein C to be activated by endogenous thrombin. The inhibition of thrombin generation (ITG) due to protein C activation could be measured by comparing thrombin formation in the presence and in the absence of thrombomodulin. ITG increased with both protein C and protein S concentrations. Normal values of ITG expressed as a percentage were between 40 and 65% and were not influenced by age or sex. ITG increased in patients under heparin therapy, decreased in patients under oral anticoagulant therapy and was decreased in women using oral contraceptives. This method could be used for screening patients for protein C and protein S deficiencies.

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SummaryThe sensitivity and specificity for deep vein thrombosis (DVT) of a new rapid, quantitative and precise (total imprecision < 10%) D-dimer assay suitable for individual measurements (VIDAS D-DIMER, bio-Merieux, France) were evaluated in a consecutive series of 103 in- and out-patients submitted to serial compression ultrasonography (C-US) for the clinical suspicion of DVT (n = 66) or of DVT recurrence (n = 37) and symptoms lasting from 1 to 15 days. DVT was found in 22 patients at baseline testing and no patient with an initially negative C-US developed vein incompressibility at follow up. The time elapsed from the onset of symptoms was negatively associated with D-dimer levels both in patients with and in those without DVT. In the entire series of patients, the sensitivity of a positive D-dimer test (≥1.0 Μg/ml) for the presence of DVT was 96% (21/22 patients, 95% confidence interval 75-100%) with a specificity of 75% (64-84%), a negative predictive value of 98% (90-100%), a positive predictive value of 51% (35-67%), and an overall accuracy of 80% (70-87%). A normal D-dimer value (0.22 Μg/ml) was observed in one patient with DVT and symptoms lasting from 15 days. The approach of withholding C-US testing in patients with symptoms lasting from less than 11 days and D-dimer levels below the cut-off value was compared to serial C-US testing alone in a cost-effectiveness analysis subdividing the 66 patients with a first episode according to their clinical pretest probability of DVT. Thrombosis was detected in 6.7% of the patients in the low probability group (n = 15), 16.7% of the patients in the moderate probability group (n = 24), 51.9% of the patients in the high probability group (n = 27) and 8.1% of patients with suspected DVT recurrence. Calculated cost-savings for each DVT diagnosed ranged from 5% in the high pretest probability group to 55% in the low pretest probability group and to 77% in patients with suspected DVT recurrence.The safety of avoiding C-US testing in symptomatic patients with a negative D-dimer test should be evaluated in clinical management studies.