Clinical Importance of Positive Test Results for Lupus Anticoagulant and Anticardiolipin Antibodies.

• Objectives: To assess the performance of 4 clotting assays for lupus anticoagulant (LA) detection, to determine the prevalence of LA and anticardiolipin antibodies (aCL), and to correlate LA and aCL prevalence with systemic disease and thrombosis. • Patients and Methods: We studied 664 consecutive patients at the Mayo Clinic in Rochester, Minn, who were referred for laboratory testing because of a clinical suspicion of LA or thrombophilia between June 25, 1990, and July 1, 1991. • Results: Of 664 patients tested for LA, 584 also were tested for aCL. Of patients tested for both LA and aCL, 137 (23.5%) had positive results for one or both tests (13 [9.5%], LA-positive only; 76 [55.5%], aCL-positive only; and 48 [35.0%], positive for both). The dilute Russell viper venom time (DRVVT) was the most frequently positive LA assay (74 % of the 61 patients with positive results for LA). Twenty-two patients (36.1% of the 61) had positive results for all 4 LA assays, whereas 21 (34.4% of the 61) had positive results for only 1 LA assay: activated partial thromboplastin time (3 patients [4.9%]), plasma clot time (5 patients [8.2%]), kaolin clot time (5 patients [8.2%]), or DRVVT (8 patients [13.1%]). Thromboembolism prevalence was not definitely associated with positive test results (LA only, aCL only, or LA plus aCL), nor was it strongly associated with aCL isotype or titer. Furthermore, thromboembolism prevalence was not increased when all LA assays were positive, although a history of deep venous thrombosis or pulmonary embolism was nonsignificantly associated with positive results for all 4 LA tests. The likelihood of having both LA- and aCL-positive test results was higher among patients with systemic lupus erythematosus (26 [19.0%] of 137 patients with positive results for one or both tests), but they had no more thrombotic events or fetal loss than other patients in our study group. • Conclusions: The DRVVT identified more patients with LA than the other LA tests, but more than 1 LA test was required to identify all patients with LA. Positive results were much more common for aCL than for LA. No single LA test or anticardiolipin isotype correlated with thrombosis or systemic disease in this population. [ABSTRACT FROM AUTHOR]