Utilization of testing for activated protein C resistance in a reference laboratory.

Abstract

Activated protein C (APC) resistance is a newly described thrombotic disorder accounting for the majority of patients with inherited thrombosis. The authors prospectively evaluated laboratory testing of this disorder over a 1-year period in their reference laboratory, which draws samples from a large number of community and academic hospitals throughout the United States. Testing for other inherited thrombotic disorders (antithrombin III deficiency, protein C and S deficiencies) occurred at a six-fold greater rate than that for APC resistance. Previously published studies have indicated a prevalence of up to 60% for APC resistance in populations with thrombosis; however, the prevalence rate in this study was only 12%. Of patient samples submitted for APC resistance assays, 37% were not evaluable because of concomitant anticoagulant therapy. Clinical pathologists and practitioners need to be made aware of APC resistance and of optimal sample collection to improve the efficiency of laboratory testing for thrombosis.