Keywords
vitamin k antagonist
antiphospholipid syndrome
How to Cite
Abstract
Introduction. The detection of lupus anticoagulant (LA) in patients who are on vitamin K antagonist (VKA) treatment is still an unresolved issue. Some guidelines recommend performing all tests on the equimolar mixture of the patient's plasma plus normal plasma pool (PN+PP) in those patients with INR<3. However, the latest ISTH guideline suggests not determining LA in patients with VKA. AIM. To compare the final conclusion of LA studies, performing screening and confirmatory tests in pure plasma (PP) and in the mixture (PP+PN), in patients receiving VKA treatment. Population. 90 patients with a previous diagnosis of persistent AL, who at the time of inclusion were in treatment with VKA with INR < 3. All had been studied for a second time to confirm the diagnosis of persistent LA, three months later, under anticoagulant treatment with low molecular weight heparin and then continued treatment with VKA. Materials and methods. Screening and confirmatory tests of Russell's viper venom time (dRVVT and cRVVT) and silica coagulation time (sSCT and cSCT) were performed. The normal plasma pool was prepared with 40 blood donors, who were negative for the AL evaluation. The cut-off points were established locally according to the ISTH guideline. Results. 33/90 patients were LA positive considering PP and PP+PN, 27 were negative and 30 discordant. 46 of the 90 samples were positive by dRVVT in PP but only 18/90 were positive by dRVVT assay in PP+PN. The kappa value for the measure of agreement between the dRVVT test in both situations was 0.21 (95% CI = 0.047-0.374). 52/90 were negative by SCT assay in PP and 50/90 were positive in PP+PN. Only 9/90 were positive by SCT in PP+PN and negative in PP. The kappa index for the SCT was 0.638 (0.431-0.844). Discussion. Although performing LA tests on the PP+PN mixture in anticoagulated patients with VKA is a common practice, according to these results, it is not a good option because they could givea false negative or positive diagnosis, depending on the assay. The discrepancy between using or not using the mixture is greater in dRVVT´s assay.
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