Rapid D-dimer assays to exclude deep venous thrombosis and pulmonary embolism: current status and new developments.

Studies measuring the fibrin degradation product D-Dimer (DD) using enzyme-linked immunosorbent assays (ELISA) in patients suspected of deep venous thrombosis (DVT) or pulmonary embolism (PE) suggest that it is possible to exclude DVT/PE when the DD level is below a certain cut-off value. However, ELISA methods are time-consuming, bare high costs, and are only available in experienced laboratories. For this reason several rapid and less costly DD assays have been recently developed. This article reviews the current literature about rapid latex and ELISA DD assays in the diagnostic approach of DVT and PE. Two new latex assays seem suitable in clinical practice. The most extensively studied assay is the so-called SimpliRed DD, an autologous red cell agglutination test that can be performed on fresh whole blood. For DVT a sensitivity (Sens) and a negative predictive value (NPV) of 89-100% and 95-100%, respectively, have been reported, for PE 94-100% and 98-100%, respectively. The second test, Tinaquant, is a quantitative latex assay. Sens and NPV for DVT of 99% and 93% have been reported in one study. Two rapid ELISA assays have been investigated. The most extensively studied is the VIDAS DD assay, a fully automated quantitative ELISA method. Sens and NPV of 94-100% and 92-100% for DVT and both 100% for PE have been reported. For the other rapid ELISA, Instant IA DD, Sens and NPV of 92-93% and 76-77% have been reported for DVT. The last one is a qualitative assay giving only positive or negative results. These results show that low concentrations of plasma DD measured by especially SimpliRed or VIDAS DD, might be used to reliably rule out DVT or PE in clinically suspected patients. Tinaquant seems promising and has to be evaluated further. As for standard ELISA, increased DD concentrations are of no use because of the low specificity of the assays. Future studies should assess the clinical usefulness of both assays in management trials under routine conditions, in the frame of clinical decision-making diagnostic processes to prove that withholding further noninvasive testing and/or anticoagulants in patients with a low or negative DD is safe. Strategies to identify patients with false-negative results should be developed.