Evaluating laboratory approaches to the identification of lupus anticoagulants: a diagnostic challenge from the RCPA Haematology QAP

Background: Laboratory identification of lupus anticoagulants (LA), an important component of the clinical diagnosis of the autoimmune disorder antiphospholipid syndrome (APS), is challenged by the heterogeneity of tests available, the diagnostic and laboratory approach undertaken, and the heterogeneity of the autoantibodies present. Aim: To assess the laboratory approach for investigation of LA, as well as the utility of various tests and test approaches, given a difficult clinical scenario in which LA might or might not be present. Methods: Ninety-three participants in the Royal College of Pathologists of Australasia (RCPA) Haematology Quality Assurance Program (QAP) were sent 4 mL of a complex but strongly positive LA sample blinded to the nature of the abnormality. Results: Seventy-three (79%) participants returned results and in most cases diagnostic interpretations. The laboratory approach to LA investigation of this sample was quite varied: 34.7% of participants concluded the sample was LA negative, with 91.7% of these performing dilute Russell viper venom time (dRVVT) testing without mixing, whereas 43.5% of participants identified a strong LA, with 96.7% of these having performed mixing studies. Most laboratories reporting negative LA instead identified the false presence of specific factor inhibitors against a variety of factors, including II, V and VIII. Conclusions: For this difficult challenge, performance of non-mixing dRVVT was associated with a high false negative LA rate.