Abstract

Various tests have been advocated for the detection of lupus like anticoagulants (LA) and related antiphospholipid antibodies, but there is no agreement on the most appropriate laboratory approach. Two hundred and fifty five of 433 hospital centres in the United Kingdom responded to a questionnaire. Many different tests were reported to be in use for screening for LA with considerable variation in plasma preparation, choice of reagent, and methodological details. Three freeze dried plasmas were subsequently assessed for the presence of LA by 183 laboratories. While 92% correctly identified a strong inhibitor and 91% a negative control, only 65% correctly identified a weak inhibitor. Pronounced variations in the suitability of commonly used reagents in the activated partial thromboplastin time test (APTT) were noted and important methodological features were identified in the kaolin clotting time, dilute thromboplastin time, and dilute Russell's viper venom time tests. It is concluded that careful plasma preparation, with avoidance of platelet contamination, use of a suitable test in addition to the APTT, and attention to methodological detail are essential for the reliable identification of LA, a clinically important inhibitor.