From Dr. Ning Tang:
Hi, George, We have a patient with strong lupus anticoagulant (LAC or LA). Diluting the plasma can’t recover the intrinsic factor activities (all <20%), also all results of the intrinsic factor inhibitors were positive. Hence we replaced the APTT reagent by a silica clotting time reagent that contains sufficient phospholipid and is used as confirmatory test for LA, and built new factor and factor inhibitors calibration curves. From them we got normal intrinsic factors activities and negative inhibitors results for the patient plasma. Do you think this method is credible? Thank you!
Hello, Dr. Tang, and thank you for your question, which I discussed with my colleague and coagulation expert, Dave McGlasson, MLS. We agree that your approach is acceptable, provided you have adequately validated the confirmatory reagent and method. According to Pengo V, Tripodi A, Reber G, et al, Update of the guidelines for lupus anticoagulant detection. J Thromb Hemost 2009; 7: 1737–40, the PTT reagent that is most sensitive to LA provides silica as its activator and has a low phospholipid content. Pengo and colleagues suggest that ellagic acid activator is not sufficently sensitive to LA and should not be employed for LA detection. Having established the presence of LA, if there is reason to measure procoagulant levels, a PTT reagent with intermediate or low LA sensitivity is necessary, and if the initial PTT result using this reagent is prolonged, the specimen should be diluted to the point where the LA effect is lost so that the operator may estimate the procoagulant levels. I hope this is helpful.