Molecular testing for the factor V-Leiden mutation in the clinical laboratory

Activated protein C (APC) resistance is a major cause of deep venous thromb osis. Most cases of APC resistance are due to a variant of factor V (FV), k nown as FV-Leiden, that is resistant to degradation by APC. The FV-Leiden m utation can be detected by a simple and reliable polymerase chain reaction method. During the past year we tested 355 patients for FV-Leiden. Twenty-s ix were heterozygous, and 3 were homozygous for the mutation. The prevalenc e of FV-Leiden was substantially higher in patients <30 years of age.