D-dimer testing is widely used in conjunction with clinical pretest probability (PTP) for venous thromboembolism (VTE) exclusion. We report on a multicenter evaluation of a new, automated, latex enhanced turbidimetric immunoassay [HemosIL D-Dimer HS 500, Instrumentation Laboratory (IL)].
747 consecutive outpatients with suspected proximal deep vein thrombosis (DVT, n=401) or pulmonary embolism (PE, n=346) were evaluated at four university hospitals in a management study with a 3 month follow-up. Samples were tested at each center using the new D-dimer assay on an automated coagulation analyzer [ACL TOP (IL)], with clinical cut-off for VTE at 500 ng/mL (FEU).
The sensitivity and negative predictive value (NPV) were 100% for all PTP subgroups (no false negative results); for both sensitivity and NPV the lower limit of the 95% CI in patients with moderate/low PTP was higher than 95%. The overall specificity was 45.1% (95%CI: 41.1-49.3%). Higher specificity value was recorded in the low PTP subgroup [49.2% (95%CI: 41.7-56.7)]. No significant differences were found between patients suspected of having DVT or PE; sensitivity and NPV were 100%. The reproducibility of the assay was good, being the total CVs% less than 10% for D-dimer concentration near the clinical cut-off.
The new, highly sensitive D-dimer assay proved to be accurate when used for VTE diagnostic work-up in outpatients. Based on 100% sensitivity and NPV and lower limit of the 95% CI higher than 95%, the assay can be used as a stand-alone test in patients with non high PTP.