THE THROMBOTIC DIATHESIS ASSOCIATED WITH THE PRESENCE OF PHOSPHOLIPID ANTIBODIES MAY BE DUE TO LOW-LEVELS OF FREE PROTEIN-S

PURPOSE: To determine if abnormalities in the protein C/protein S anticoagulant system exist in patients with phospholipid antibodies who had the primary clinical complaint of fetal wastage. PATIENTS AND METHODS: Eleven patients with fetal wastage and phospholipid antibodies were selected for study Some patients also gave a history of previous thrombotic events related to oral contraceptives and/or pregnancy, but patients were not selected because of a history of clinical thrombosis. The levels of protein C (chromogenic assay), protein S (both free and bound) (Laurell rocket), and C4b-binding protein (Laurell rocket) were measured, and assays for the presence of antibodies against protein S or protein C were performed. RESULTS: Seven of the 11 patients were found to have low levels of free protein S. Total protein S and protein C levels were within the normal range in all patients. Antibodies to protein C and protein S were not found in any patient. These findings suggest that free protein S levels may be abnormally low in some patients with phospholipid antibodies. CONCLUSION. Free protein S levels are abnormally low in some patients with phospholipid antibodies, and this abnormality may be a factor contributing to the thrombotic diathesis associated with phospholipid antibodies.