Summary
In 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.
