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?