MULTICENTER EVALUATION OF A KIT FOR ACTIVATED PROTEIN-C RESISTANCE ONVARIOUS COAGULATION INSTRUMENTS USING PLASMAS FROM HEALTHY-INDIVIDUALS

Recently a new hemostatic disorder has been described which appears to be an important risk factor for familial thromboembolism. The disorde r is characterized by a poor anticoagulant response to activated Prote in C (APC) and has been shown to be due to lack of an APC cofactor act ivity which is a property of factor V. A kit for determining the respo nse of plasma samples towards addition of APC in an APTT-based assay - COATEST APC Resistance has been evaluated on 35 coagulation instrumen ts in a multicenter study involving 32 laboratories. A lyophilized nor mal plasma and identical plasma aliquots from 20 individuals, one of w hom had a borderline resistance to APC, were analysed in each laborato ry and the sensitivity of each plasma to APC was determined as the rat io between the clotting times obtained in the presence and absence of APC (APC ratio). The plasma from the individual with a borderline resi stance to APC activity was correctly classified as the lowest responde r in each laboratory, with an APC ratio in the range 1.6-2.4. fn compa rison, plasmas from individuals with a pronounced response to APC acti vity resulted in APC ratios above 3.4 in most cases. interestingly, al though the actual APT time for a plasma from a given individual showed a more than 10 s difference due to the type of instrumentation used, the variation in the APC ratio was limited. A similar discrimination w as also obtained from evaluation of the actual prolongation of the clo tting time in the presence of APC. The intra-laboratory coefficient of variation for the clotting times were on average 2.0% and 3.9% in the absence and presence of APC, respectively, indicating that the precis ion for the prolonged clotting times obtained in the presence of APC i s sufficient to allow a safe assignment of the APC response. The APC r atio for the lyophilized normal plasma was 2.7 +/- 0.2 (2 S.D.) illust rating a narrow distribution between instruments which shows the feasi bility of including such plasma for assay validation. Altogether, the results indicate that all the coagulation instruments included in the study can be used for detection of individuals with resistance to APC activity through determination of the APC ratio or the prolongation ti me.