Standardization of the measuring method for lupus anticoagulant (LA)

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Standardization of the measuring method for lupus anticoagulant (LA), which is a risk factor of thrombosis, was investigated. The plasma (residual platelets: less than 3,000/uL) obtained by single centrifugation at 1500 x g for 15 minutes, is quite useful for LA tests, because LA activity was significantly changed in plasma with more than 1,200/uL of residual platelets. On the other hand, the sensitivity of APTT reagents for LA is dependent on phospholipid concentration and not the activator, according to our results of LA activity using APTT reagents with same phospholipid condition and silica or ellagic acid as a activator. In an APTT cross-mixing test, 10% and 20% ratio of LA plasma and a 50% ratio of factor VIII deficient plasma or inhibitor positive plasma produced optimum results. Therefore, it is recommended to carry out the mixing test on 5 different mixing ratios of 0, 10, 20, 50, 100% of patient plasma.