I had the pleasure of meeting Norbert Bennattar, Directeur General of Cryopep, Montpellier, France while attending the International Society on Thrombosis and Haemostasis biennial meeting in Amsterdam, July 1–4, 2013. Mr. Bennattar posed a question I couldn’t answer. When performing the dilute Russell viper venom time (DRVVT) assay for lupus anticoagulant (LA), the operator begins with a screening assay. When prolonged above the upper limit of the reference interval, the operator then follows up with a high-phospholipid confirmatory reagent. The results of the confirmatory assay are expected to be shorter than the screen, owing to the higher concentration of phospholipid, and if the ratio of screen to confirmatory assay exceeds 1.2 (or a locally computed ratio that is close to 1.2), LA is confirmed. However, Mr. Bennattar reported on instances in which the patient’s screen was prolonged and confirmatory reagent produced a result that was longer than the screening assay (creating a ratio <1), and he asks, what may account for this, and is this a common occurrence?
Jul 16 2013
Hello professor, my name is Marcelo Goncalves
Hello professor, my name is Marcelo Goncalves. I´m a clinical pathologist from Brazil and we used to perform 500 LA tests per week. I had the same results in 2009-10 as related by Mr. Bennattar but using HemosIL silica clotting time. The confirmatory reagent produced a result that was longer than screening test. It wasn´t a lot number-dependent problem. I discussed these results with some colleagues but without a explanation for the facts. Please, let me know if you have possible explanations that may account for these facts. Thank you for opening the discussion.