Patterns of anti-phospholipid antibody specificities.

To determine the importance of assaying for anti-phospholipid (PL) antibodies other than anti-cardiolipin antibodies in patients with putative anti-phospholipid antibody syndrome (APA), 1,513 serum samples from over 399 patients with the potential for thromboembolic disease were tested for IgM, IgG or IgA class antibodies to the following phospholipids: cardiolipin, phosphatidylserine, phosphatidylinositol, phosphatidylethanolamine, phosphatidylglycerol and phosphatidic acid. Non-specific binding was subtracted from total binding of antibodies to each PL to eliminate false positive ELISA results. Only patients whose sera contained antibody levels which were greater than three standard deviations above the means were considered positive. Patients who were positive for anti-PL antibody had antibodies to at least one of six phospholipids tested. Approximately 60% of the positive samples contained antibodies to a phospholipid other than cardiolipin. For IgG class, antibodies to phosphatidylserine were the most prevalent followed by antibodies to phosphatidylethanolamine and cardiolipin. These findings indicate that anti-phospholipid antibody analysis should be performed for more than anti-cardiolipin antibody to detect patients with APA.