The International Society on Thrombosis and Haemostasis and the Clinical and Laboratory Standards Institute agree that the lupus anticoagulant (LAC ) test profile should employ two testing platforms, and both recommend, among other choices, an assay based upon the dilute Russell viper venom time (DRVVT ) and a second assay based on the PTT.
Each platform employs a low phospholipid reagent sensitive to LAC
as the first-tier or "screen" stage and a second, high phospholipid "confirm" reagent. Some experts advocate for normalization in which the two results for each platform are normalized to the MRI
in this formula: Normalized ratio = (screen result/MRI) / (confirm result/MRI). Others prefer the simpler formula, Ratio = screen results/confirm results, and still others prefer s simple difference in seconds. Our October, 2018 Quick Question polls our participants on these preferences. Which formula does your laboratory apply for the DRVVT