THE LUPUS ANTICOAGULANT - HIGH-INCIDENCE OF NEGATIVE MIXING STUDIES IN A HUMAN-IMMUNODEFICIENCY-VIRUS POSITIVE POPULATION

We identified 100 patients (51 males and 49 females) as having the lup us anticoagulant. The following diagnoses were found in the patient po pulation: human immunodeficiency virus positivity, 20%; systemic lupus erythematosus, 10%; prolonged preoperative activated partial thrombop lastin time (APTT), 10%; procainamide hydrochloride-induced inhibitor, 9%; deep vein thrombosis, 6%; seizure disorders/epilepsy, 5%; and mis cellaneous conditions, 40%. Identification was based on a prolonged AP TT (>40 seconds) that normalized with increased phospholipid concentra tions and/or a prolonged Russell viper venom clotting time patient-con trol ratio of 1.20 or greater. In 68 cases (group 1), patient plasma p rolonged the APTT of normal plasma in a 1:1 mixing study. However, in 32 cases (group 2), no such prolongation was observed. There was a sig nificant difference between presenting APTTs in patients from group 1 (mean+/-SD, 58.29+/-13.30 seconds) compared with that in group 2 (mean +/-SD, 47.93+/-5.09 seconds). Furthermore, 66% of group 1 patients had elevated anticardiolipin antibody titers compared with only 41% in gr oup 2. Of the 32 patients in group 2, 16 (50%) were positive for human immunodeficiency virus. We concluded that the investigation of a lupu s anticoagulant should not be abandoned because patient plasma does no t prolong the APTT of normal plasma in a mixing study, especially in a human immunodeficiency virus-positive population.