Consultative Interpretation for Lupus Anticoagulant by Expert Pathologist Reduces False-Positive Rates in the Era of Direct Oral Anticoagulants

Background: The diagnosis of antiphospholipid syndrome requires detection of antiphospholipid antibodies (aPL). A retrospective review of our testing practices revealed that societal recommendations for lupus anticoagulant (LA) testing as part of aPL testing are largely not followed by clinicians, and there was a high proportion of positive LA results. Increasing direct oral anticoagulant (DOAC) usage creates additional challenges in identifying LA. This prompted us to establish an order set with pathologist consultation ("LA panel") and testing algorithm to reduce false-positive LA and to ensure optimal LA identification and best practices for interpretation and follow-up. Methods: The laboratory database was reviewed to determine the number of LA tests ordered and rate of LA positivity before and after the LA panel was instituted. We assessed the impact of pathologist consultation to minimize false-positive findings and on following diagnostic guidelines. Results: LA panels were ordered for 1146 patients. LA was detected in 10% (111 of 1146) by dilute Russel vipervenomtime (dRVVT) normalized ratio [includes dRVVT screen (dRVVTs) positive/lupus-sensitive partial thromboplastin time (PTT-LA) positive and dRVVTs positive/PTT-LA negative] and 20% (228 of 1146) by Staclot-LA (includes dRVVTs negative/PTT-LA positive and dRVVTs positive/confirm negative). There was a reduction of false-positive LA by Staclot-LA; previously, 48% positive. We saw increased cancellation of LA testing for interfering anticoagulants [6.8% (16 of 236) vs 14.4% (55 of 383); P = 0.0061]. There was also increased adherence to follow-up LA testing [3% (8 of 236) vs 13.8% (53 of 383); P = 0.001]. Conclusions: Creating a predetermined order set and testing algorithm with pathologist consultation improved LA testing interpretation and diagnostic follow-up testing.