The rapid whole blood agglutination d-dimer assay has poor sensitivity foruse as an exclusion test in suspected deep vein thrombosis

Aims. Several clinical studies have proposed using d-dimer as an initial sc reening test to exclude thrombosis in cases of suspected (DVT), In publishe d series, these assays have variable sensitivity, raising concerns that the y may not be sufficiently robust for clinical practice. The aim of the stud y was to examine the sensitivity of two commercially available d-dimer assa ys and to assess their value and safety as initial screening tests in suspe cted DVT, Methods. In this prospective study, blood samples were collected for d-dime r measurement (SimpliRED assay and IL test d-dimer) in all patients present ing to the emergency department over a twelve month period. All patients un derwent compression ultrasound scanning as the primary diagnostic procedure . Results. 235 patients were included in the study. 51(22.8%) had a DVT confi rmed on ultrasound. The SimpliRED assay was positive in only 33 cases, with seventeen cases of confirmed DVT giving a negative result (six cases with proximal vein thrombosis). Assay sensitivity was 66%, with a negative predi ctive value of 88.9%. The IL test gave three false negatives (all below kne e thromboses) giving assay sensitivity and negative predictive value of 94. 1% and 96.8% respectively. Conclusions. The precise role of d-dimer testing in the diagnosis of venous thrombosis has yet to be established. From our results and a review of pub lished series, we conclude that the SimpliRED assay is too insensitive to u se as a reliable exclusion test in cases of suspected DVT, however, the mor e sensitive automated IL test d-dimer may have a role in the initial assess ment. We propose that the IL d-dimer test is used in conjunction with a pre -test probability score to identify patients at low risk of DVT and recomme nd that this approach is tested in a clinical study before introduction int o practice.