Comparison of screen-confirm versus screen-mix-confirm algorithms for lupus anticoagulant detection by dilute Russell’s viper venom time

Objectives Lupus anticoagulant (LAC) is an antiphospholipid antibody associated with thromboembolism. According to the International Society on Thrombosis and Haemostasis, LAC measurement by Dilute Russell’s viper venom time (dRVVT) should follow a three-step procedure: “Screen-mix-confirm.” However, studies have raised concerns that the mixing step alters interpretation. Our aim is to assess the impact of a mixing study in LAC testing by dRVVT. Materials and Methods Patients undergoing LAC testing by dRVVT were prospectively enrolled from April 2021 to February 2022. Those who tested positive for the LA screen were tested by mixing and confirmation steps. Statistical analysis Data were analyzed using IBM® Statistical Package for the Social Sciences version 26. The chi-square test was used to assess whether the frequency of LAC positivity is significantly different with the addition of a mixing study. P < 0.05 was considered statistically significant. Results A total of 90 patients were included, with a mean age of 37 ± 14.2 years and a majority of females ( n = 52, 57.8%). Similar results with both algorithms were seen in 76 (84.4%) samples. Among the 14 (15.6%) discrepant results, majority (10 out of 14) were weak positive for LAC by the two-step method while negative for LAC by the three-step method. The chi-square test revealed a significant difference in LAC positivity with and without a performance of mixing study ( P < 0.001). Conclusions Interpretation of dRVVT with the inclusion of a mixing study leads to decreased frequency of LAC positivity. We recommend that a mixing step should not be used for weak positive LAC, to avoid discrepancies occurring due to the dilutional effect of mixing with normal plasma.