Practice and performance of lupus anticoagulant tests: A single centre experience

INTRODUCTION: Lupus anticoagulant (LA) is a well-known risk factor for thrombosis. Correct diagnosis of LA is essential in patient management with anticoagulation. The objectives of this study were to document the clinical and laboratory characteristics of patients tested for LA and to evaluate existing LA testing methods in our laboratory with the aim of improving the performance of LA test interpretation and reporting.

METHODS: Tests for LA include dilute Russell's viper venom time (dRVVT) and Kaolin clotting time (KCT). Patients with LA ratio (dRVVT screen ratio/dRVVT confirm ratio) of ≥1.2 were considered as LA positive irrespective of KCT results. KCT was considered positive if there was a prolongation in KCT screening test which was not corrected on mixing with normal plasma.

RESULTS: Of 577 patients' results, 295 were normal, 178 were KCT positive with negative dRVVT and 104 were LA positive. Incidences of thrombosis, connective tissue disease (CTD) and bad obstetric events were noted in 13%, 16% and 44% of normal patients, 9%, 22% and 49% of KCT+ patients and 23%, 37% and 17% of LA+ patients respectively. On further evaluation of dRVVT screen ratios, 431 had a ratio of <1.1, 59 had a ratio between 1.1 and 1.2 and 87 had a ratio of >1.2. Positive LA results were found in 3%, 29% and 87% of patients with dRVVT screen ratios of <1.1, 1.1 - 1.2 and >1.2 respectively.

CONCLUSION: LA+ patients had higher incidences of thrombosis and CTD as compared to normal and KCT only positive patients. There was no significant difference in clinical characteristics between normal and KCT+ patients which suggests the presence of a high rate of false-positive KCT results. Since confirmatory testing for KCT is not widely used, the option of using another LA screening test method should be considered. In regard to dRVVT testing, confirmatory test should only be performed in patients with prolonged dRVVT screening result which was not corrected upon mixing with normal plasma as required by the International Society of Thrombosis and Haemostasis guidelines on LA testing. This practice will not only result in significant cost reduction but also avoid diagnostic confusion.