The utility of the Taipan snake venom assay in assessing lupus anticoagulant status in individuals receiving or not receiving an oral vitamin K antagonist

Abstract

The objective of the present study was to evaluate the Taipan snake venom time (TSVT) assay in the detection of lupus anticoagulant in patients receiving or not receiving oral vitamin K antagonists. Blood samples were collected from individuals requiring investigation for the presence of a lupus anticoagulant. The TSVT test was run in parallel with the dilute Russell viper venom time (dRVVT) assay and anticardiolipin antibody assays. Results were assessed by Bayesian statistics. Two thousand and five plasma samples were obtained from 1335 individuals. One thousand, one hundred and eleven individuals were not receiving oral vitamin K antagonists; of these, 451 had a lupus anticoagulant by conventional testing, and the TSVT showed a sensitivity of 22%, specificity of 98%, positive predictive value of 80%, negative predictive value of 78%, positive likelihood ratio of 12.3 and a negative likelihood ratio of 0.790. Two hundred and ten of the 224 patients receiving oral vitamin K antagonists were known to have a persistent lupus anticoagulant prior to oral anticoagulation. In this setting, TSVT had a sensitivity of 39% and specificity of 93%, but the dRVVT had a 50% false-positive rate, which meant that despite having a higher sensitivity at 61% than the TSVT, its specificity was only 53%. TSVT is a specific but insensitive assay for the lupus anticoagulant in individuals not receiving oral vitamin K antagonists, when assessed against the dRVVT as the gold standard. It can be argued that despite the TSVT's poor sensitivity in patients taking oral vitamin K antagonists, its high specificity and positive predictive value make it a preferable assay to the dRVVT to diagnose lupus anticoagulant in this group.