Improved confirmation of weak lupus anticoagulants by employing sensitive and insensitive reagents to the lupus anticoagulant

Detection of a lupus anticoagulant (LA) is of major importance to detect a thrombotic tendency. Confirmation of its phospholipid dependency may repres ent a tricky step in the diagnostic algorithm for LA, as several tests may yield borderline results of little diagnostic help. To improve on this poin t, we had previously employed a procedure comparing sensitive [rabbit brain kaolin (RBK)] and insensitive [soy bean phosphatides (SBP)] reagents to LA to screen and confirm LA at the same time in activated partial thromboplas tin systems (aPTT). Here we compared its performance against a platelet neu tralization procedure (PNP). To allow comparisons of our procedures with th e PNP, a percentage ratio correction was calculated according to the follow ing formula: [(RBK ratio - SBP ratio) X 100]/ RBK ratio. Similarly for the PNP: percentage ratio correction = [(buffer ratio - platelet phospholipid r atio) X 100]/buffer ratio. On 44 known LA plasmas, the PNP, expressed in se conds, yielded 15 (34%) negative or borderline results. After ratio transfo rmation, the PNP still yielded 10 of 15 (66%) uncertain results, whereas th e RBK/SBP procedure did not give any uncertain results (P = 0.0002). The me an percentage ratio correction was far superior for the RBK/SBP procedure t han for the PNP (53.24 +/- 15.93 versus 20.28 +/- 12.15%, P < 0.0001). The use of sensitive and insensitive reagents to the lupus, anticoagulant incre ases the confirmatory yield of LA in aPTT systems and may deserve inclusion amongst the confirmatory procedures for its diagnosis. (C) 2001 Lippincott Williams & Wilkins.