DISCRIMINATION BETWEEN NORMAL WILDTYPE AND CARRIERS OF COAGULATION-FACTOR V LEIDEN MUTATION BY THE ACTIVATED PROTEIN-C RESISTANCE TEST IN THE PRESENCE OF FACTOR-V DEFICIENT PLASMA

Blood samples from 104 patients with clinically suspected thrombophili a were analyzed for coagulation factor V Leiden mutation (1691, G-->A) by allele-specific polymerase chain reaction. In 86 individuals (82.7 %), the mutation was not detectable, whereas 15 patients (14.4%) were heterozygous and three patients (2.9%) were homozygous for factor V Le iden mutation. Plasma samples from these individuals were also tested for functional resistance of coagulation factor V to activated protein C (activated protein C resistance). This test was performed on a Schn itger-Gross coagulometer using an activated partial thromboplastin tim e-based activated protein C resistance test modified by applying a 1:5 dilution with factor V-deficiency plasma. All the individuals negativ e for factor V Leiden mutation were also negative in the functional ac tivated protein C resistance test. On the other hand, all patients car rying the mutation revealed pathologic results in the activated protei n C resistance test. The cutoff value for the activated protein C resi stance index (greater than or equal to 1.7=negative) was determined by testing 31 male and female blood donors. One of them was heterozygous for factor V Leiden mutation and had an activated protein C resistanc e index of 1.4, whereas those without factor V Leiden mutation had an activated protein C resistance index of 1.9+/-0.1 (<(x)over bar+/-SD>) . Patients with clinically suspected thrombophilia without factor V Le iden mutation had an activated protein C resistance index of 2.1+/-0.2 (<(x)over bar+/-SD), whereas patients heterozygous for the mutation h ad an index of 1.5+/-0.1 (<(x)over bar+/-SD>). Within the group of pat ients carrying the mutation, the activated protein C resistance test e ven distinguished between heterozygous and three homozygous (activated protein C resistance 1.0 to 1.2) carriers. The data demonstrate that the activated protein C resistance test in the presence of factor V-de ficiency plasma provides a clear-cut discrimination between normal wil dtype and carriers of factor V Leiden mutation with a sensitivity and specificity of 100%. Verification of positive activated protein C resi stance tests can be performed easily with a simple and reliable polyme rase chain reaction protocol for the 1691, G-->A mutation.