INTRODUCTION: To rule out the presence of LA antibodies, two or more assays that are sensitive to these antibodies must be negative. The dilute Russell’s Viper Venom Time (dRVVT) and the activated partial thromboplastin time (aPTT) using sensitive reagents have been employed to detect LA. The aim of this study was to assess the concordance level of aPTT using Platelin LS and dRVVT as screening tests to identify LA in patients with venous thromboembolism (VTE).

METHODS: 94 patients (58 women, 62%) with VTE were evaluated. The detection of circulating inhibitor with Platelin LS and dRVVT was based on a prolonged clotting time and a prolonged 1:1 mixture of sample plasma and normal pooled plasma. The confirmation of the phospholipid dependency was performed only with dRVVT.

RESULTS: Among the 94 patients, an abnormal test was found in 24 patients (26%) with aPTT and in 61 patients (65%) using dRVVT. After mixing tests, aPTT ratio remained long in 25% of patients with abnormal aPTT, and in 9.8% with long dRVVT. Five patients had a prolonged mixing study identified by both tests, which resulted in a substantial agreement between the two tests (Kappa= 0.78). Confirmatory tests for LA were positive in 5 out of the 6 patients with long dRVVT mixture, resulting in a prevalence of LA detected by dRVVT of 5.3%. The 5 patients with LA detected by dRVVT also had prolonged mixture with aPTT.

CONCLUSION: Our results indicate that aPTT with Platelin LS is highly associated with the presence of LA detected by dRVVT and may be suitable as a screening test for LA in patients with VTE.

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