Comparison Between a One-Point Dilute Phospholipid APTT and the Dilute Russell Viper Venom Time for Verification of Lupus Anticoagulants

Abstract

SummaryIn the present study, the dilute Russell viper venom time (RVVT) and the dilute phospholipid activated partial thromboplastin time (PL-APTT), which are two assays used for the verification of lupus anticoagulants (LA), were modified to increase standardization. The modified assays were then compared with respect to sensitivity and specificity in detecting LA in plasmas from 72 patients with a prolonged APTT. Modifications included utilizing a single dilution of phospholipid that was either bovine brain thromboplastin (Thrombofax) or liposomes comprised of phosphatidylcholine/phosphatidylserine, and expressing the results as a ratio of the clotting times of the mixture of patient and normal plasma/clotting time of normal plasma. In the RWT, the correlation coefficient between assay results for liposomes and Thrombofax was 0.88 and in the PL-APTT, the correlation was 0.68. A positive test for LA was defined as a ratio of ≥1.3 for the PL-APTT with liposomes and ≥1.2 for the PL-APTT with Thrombofax and the RWT with Thrombofax or liposomes. Regardless of the phospholipid source in the test system, the PL-APTT demonstrated higher sensitivity and the RWT showed greater specificity in detecting patient plasmas that contained antiphospholipid antibodies.