The laboratory diagnosis of lupus anticoagulants.

With the well-documented association of lupus anticoagulants with thrombotic disease and recurrent spontaneous abortion, the laboratory approach to diagnosing these inhibitors is more critical now. To this end, we examined plasma samples from 21 patients who initially presented with a prolonged prothrombin time or activated partial thromboplastin time or both for the presence of lupus anticoagulants. We used a battery of coagulation tests, including both immediate and two-hour mixing studies, a platelet neutralization procedure, a tissue thromboplastin inhibition test, and dilute Russell viper venom times. Two patients (10%) had only a prolonged prothrombin time, seven (33%) had only a prolonged activated partial thromboplastin time, and in 12 (57%) both were abnormal. In 15 patients, inhibition was evident on immediate assay of equal-volume mixture studies of patient plasma and normal pooled plasma, but in three additional patients it was evident only after a two-hour incubation. Fifteen of 18 samples showed correction of the abnormal screening study when platelets were used as a source of phospholipid. Both the tissue thromboplastin inhibition test and dilute Russell viper venom times were sensitive assays, being abnormal in 20 of 21 and 13 of 14 samples, respectively. In four patients, discordance of studies necessitated specific coagulation factor levels being measured to confirm the presence of the inhibitor. Because of the variable effect of the inhibitors on all currently available assay procedures, we would suggest that any evaluation will require a laboratory to have a battery of tests available before such an inhibitor can be excluded.