Screening for lupus anticoagulants in patients treated with vitamin K antagonists.

Abstract

The dRVVT test for detecting lupus anticoagulants (LA) is difficult to interpret when patients are treated with vitamin K antagonists (VKA). We performed LA testing in 33 VKA-treated patients with definite antiphospholipid syndrome (APS) and compared the results with 100 controls subjects not receiving VKA and 110 APL-negative patients anticoagulated for reasons other than APS. Compared with the dRVVT ratio before the initiation of VKA therapy, a higher cutoff value, defined as the 99th percentile, was established for VKA-treated patients with INR values between 2.0 and 3.5. A dRVVT ratio of >1.7 yielded a sensitivity of 81.3%, specificity of 99.1%, and positive and negative predictive values of 98.7% and 85.8%, respectively, for detecting LA. Cohen's kappa coefficient indicated good agreement for the dRVVT ratio obtained from testing with and without VKA treatment (κ = 0.813; 95% CI: 0.773-0.853), which was higher (κ = 0.941; 95% CI: 0.917-0.965) when the LA diagnosis was based on the results of both the dRVVT and a second test system (i.e., Mixcon-LA assay). Lupus anticoagulants testing in VKA-treated patients with APS according to current guidelines appears to be possible for the majority of patients without discontinuing anticoagulant therapy.