Abstract
Background: The classic test for determination of APC resistance (APCR) is based on the prolongation of the APTT after addition of activated protein C. The test predictability for the presence of factor V Leiden is improved by pre-dilution of the sample plasma with f.
V deficient plasma. The ProC Ac R is an innovative assay based on the prolongation of the RVVT after the incubation with the snake venom Protac, which is an activator of endogenous protein C.
Methods: Patients: 90 patients taking warfarin, in whom the termination of therapy was scheduled; 10 of them were heterozygous carriers of factor V Leiden. The blood samples were obtained before and 6 weeks after termination of warfarin.
Methods: The APCR was determined using the Coatest APC Resistance (Chromogenix), Coatest APC Resistance V S (Chromogenix) and ProC AC R assay (Siemens); the results were expressed as the ratio. Protein C was determined using clotting-based and chromogenic assays, protein S activity was determined with clotting-based assay and free protein S concentration was measured by ELISA.
Factor VIII activity was determined using clotting-based and chromogenic assays. Results: The APCR ratio during the warfarin therapy was signi fi cantly higher using the Coatest APCR assay (P < 0.001), not significantly different using the Coatest APCR VS assay and significantly lower using the ProC AC R assay (P < 0.001) than the APCR ratio after termination of warfarin.
The APCR ratio in patients on warfarin was dependent (using multivariate analysis) on the INR value (P < 0.001) and on the presence of f. V Leiden (P = 0.018) using Coatest APCR assay, on the f.
V Leiden (P < 0.001) and protein S activity (P = 0.002) and free protein S (P = 0.045) using Coatest APCR VS assay, and on the f. V Leiden (P < 0.001), protein C activity (clotting assay P = 0.008, chromogenic assay P = 0.009) using the ProC AC R assay.