Lupus anticoagulant testing: performance and practices by north american clinical laboratories.

Lupus anticoagulant (LAC) testing is important for evaluating patients with antiphospholipid syndromes and hypercoagulable states. We reviewed results of proficiency testing challenges (n = 5) distributed by the North American Specialized Coagulation Laboratory Association to examine LAC testing performed by participating laboratories. The activated partial thromboplastin time (APTT) and dilute Russell viper venom time (dRVVT) constituted major testing methods. In screening studies, LAC-sensitive APTT methods were more sensitive to weak LAC than dRVVT-based methods but less specific. In confirmatory testing, dRVVT methods performed better, but performance was LAC-dependent. The highest false-negative confirmatory test results were obtained for the platelet neutralization procedure. Noncompliance with recommendations for LAC testing by the International Society on Thrombosis and Haemostasis was high (8%-38%), with the majority of noncompliant laboratories failing to report results of mixing studies. These data provide new insights into LAC testing in North America and identify opportunities for standardization.