THE CLINICAL-APPLICATION OF A NEW SPECIFIC FUNCTIONAL ASSAY TO DETECTTHE FACTOR-V-LEIDEN MUTATION ASSOCIATED WITH ACTIVATED PROTEIN-C RESISTANCE

Resistance to activated protein C (APC) is the most common defect foun d in patients who have venous thromboembolism. The molecular basis of APC resistance is a single-point mutation (arginine(506)-glutamine) in the gene that encodes for coagulation factor V. This mutation results in a factor V molecule (factor V-Leiden) that is less effectively dow nregulated by AFC than is normal factor V. The gold standard for the d etection of this defect is DNA analysis. Several functional tests, whi ch are based on activated partial thromboplastin time clotting assays, are also commercially available for the detection of AFC resistance. These tests, however, have not been satisfactory. Compared with the re sults of DNA analysis, the results of these tests are frequently disco rdant. Further, in some patients (eg, those who have lupus anticoagula nt or have been receiving heparin), these tests cannot be performed at ail. DNA analysis is therefore required in most patients to distingui sh congenital APC resistance (factor V-Leiden) from other causes of ab normal response in functional APC-resistance tests. The purpose of thi s study was to investigate the clinical use of a new chromogenic APC-r esistance assay that is based on direct measurement of the effect of A FC on factor Va cofactor activity in highly diluted, thrombin-activate d plasma specimens. All individuals who provided plasma samples for th e study underwent DNA analysis to detect the presence of the factor V mutation. In all patient subgroups, including patients who had lupus a nticoagulant and those who were receiving unfractionated heparin or co umarin derivatives, the chromogenic test showed excellent discriminati on between normal individuals and those who were heterozygous or homoz ygous for the factor V-Leiden mutation. No discordant results with DNA analysis were found in 150 cases. The new test easily can be incorpor ated in any laboratory that has an automated coagulation apparatus wit h an option for chromogenic measurements. All reagents are commerciall y available at low cost, and the test is easy to perform and is not ti me-consuming. This new, sensitive, and specific test allows large-scal e screening for the factor V-Leiden mutation without the need for DNA analysis.