Determination of cut-off threshold of normalized ratio for determining lupus anticoagulant in normal plasma of donors – healthy volunteers (large network laboratory study results)

Laboratory tests for lupus anticoagulant (LA) are necessary for antiphospholipid syndrome (APS) diagnosis. Due to antibody heterogeneity, there are two test systems recommended to maximize detection rates: one of them is the dilute Russell’s viper venom time (dRVVT) and the second one is the activated partial thromboplastin time (APTT). Current guidelines recommend getting the reference ranges and cut-off of the normalized screen/confirm ratio in dRVVT and APTT in every laboratory. The aim of this work is establishing of reference ranges and cut-off for the normalized ratio in dRVVT and APTT reagents using two type of sample preparation. The cut-off values of LA1/LA2 (37 °C, 30 minutes), LA1/LA2 (22–25 °C, 30 minutes), Actin FSL/Actin FS (37 °C, 30 minutes) and Actin FSL/Actin FS (22–25 °C, 30 minutes) pairs in the normalized ratio were 1.21, 1.18, 1.07 and 1.08, respectively.