A latex D-dimer reliably excludes venous thromboembolism

Background: D-Dimer, a cross-linked fibrin degradation product, has a high sensitivity in patients with suspected venous thrombosis. Traditional latex D-dimer assays, however, have not been sufficiently sensitive to exclude v enous thromboembolism. Methods: To determine the clinical utility of a latex D-dimer assay (MDA D- Dimer; Organon Teknika Corporation, Durham, NC) in patients with suspected venous thromboembolism, we conducted a retrospective cohort study involving 595 unselected patients at 4 tertiary care hospitals. Patients had blood d rawn for performance of the D-dimer assay and underwent objective testing f or venous thromboembolism. Pretest probability was determined using validat ed models in 571 patients. Patients were classified as venous thromboemboli sm positive or negative according to results of objective tests and 3-month follow-up. The sensitivities, specificities, predictive values, and negati ve likelihood ratios of the assay were calculated for all patients and for subgroups of patients with known cancer or a low, moderate, or high pretest probability of venous thromboembolism. Results: The prevalence of venous thromboembolism was 19.0% (113/595). Of t hose who had a pretest probability assessment, 35.9% had a low pretest prob ability, 49.7% a moderate pretest probability, and 14.4% a high pretest pro bability. Using a discriminant value of 0.50 mug fibrinogen equivalent unit s per milliliter, the assay showed an overall sensitivity of 96%, a negativ e predictive value of 98%, a specificity of 45%, and a negative likelihood ratio of 0.09. In patients with a low or moderate pretest probability, the sensitivity, negative predictive value, and negative likelihood ratio were 97%, 99%, and 0.07,respectively. Conclusions: The MDA D-Dimer assay is the first latex agglutination assay w ith sufficient sensitivity to be clinically useful in the exclusion of veno us thromboembolism. A negative result has the potential to be used as the s ole test to exclude venous thromboembolism in patients with a low or modera te pretest probability of disease.