TECHNICAL AND BIOLOGICAL CONDITIONS INFLUENCING THE FUNCTIONAL APC RESISTANCE TEST

Poor anticoagulant response to APC is conveniently screened by a comme rcially available functional test (Coatest(R) APC Resistance) allowing identification of APC-resistant patients. These patients may then be genotyped with respect to factor V, the Arg --> Gin mutation being the principle cause of APC resistance. However, determination of phenotyp e generally precedes that of genotype, and the need for an ''abnormali ty threshold'' prompted a study of inter-batch variations and the clin ical conditions associated with an altered APC response. The response to APC was assessed twice in plasma from 111 patients using two of fou r successive kit batches. A modest but significant inter-batch variabi lity was observed. At the same time, we also tested 130 patients with retinal venous occlusion (RVO), 28 patients with glaucoma and 24 norma l volunteers. The APCaPTT/aPTT ratio was found to be lower in the pres ence of elevated thrombin-antithrombin complexes (r = 0.167, p <0.02) and low blood viscosity (at high shear rate: r = 0.305, p <0.0001) ind ependently of any alteration in genotype.