[Cross-mixing test to detect lupus anticoagulant for diagnosis of antiphospholipid syndrome].

The activated partial thromboplastin time (APTT) is generally used to screen for intrinsic coagulation factor deficiency. APTT prolongation suggests a bleeding tendency, although it can also reveal the presence of lupus anticoagulant (LA), which is one of the antiphospholipid antibodies associated with a high risk of thrombosis. Therefore, differential diagnosis in patients with a prolonged APTT is important. Recently, a cross mixing test has been proposed as a useful laboratory examination for differential diagnosis in these patients. When a cross-mixing test utilizes a mixture of patient and normal plasma at various ratios, the APTT value of the control plasma is prolonged by the addition of a small amount (10-20%) of the plasma from a patient with LA, while a prolonged APTT in a patient with an intrinsic coagulation factor deficiency is shortened by the addition of control plasma(50%). We obtained more favorable results for LA detection with a cross mixing test by measuring APTT in 5 different mixtures of control plasma and 0, 10, 20, 50, and 100% concentrations of patient plasma with an LA-sensitive APTT reagent such as PTT-LA. Also, we utilized a 0.2 microm filter unit to remove residual platelets from both patient and control plasma samples, which we recommend as useful. We found that a cross-mixing examination with appropriate samples and reagents contributed to the detection of LA. However, some problems remain regarding the final determination and quantitative measurements of LA.