The relationship between lupus anticoagulants and antibodies to phospholipid

The relationship between lupus anticoagulants and antibodies directed against negatively charged phospholipids, as measured by an enzyme-linked immunosorbent assay, was explored in a series of plasma samples from 100 patients with well-characterized lupus anticoagulants. Only 73% of the patients had detectable IgG, IgM antibodies, or both, to one or more of four phospholipids. Of these patients, 29% had IgG-type antibodies only, 56% had both IgG and IgM antibodies, and 15% had IgM antibodies only. Of the 100 patients, 19% had a history of thrombosis, 8% had a history of spontaneous abortion, and 6% had a history of seizure disorder. These complications occurred in the presence (80%) and absence (20%) of detectable antiphospholipid antibodies. Drug-related antibodies were observed in 34 patients; of these, 71% had detectable anti-phospholipid antibodies and 24% had a history of thrombosis. There were ten patients with lupus anticoagulants associated with infections; none of these patients had a history of thrombosis. The results indicate that antiphospholipid antibodies are not present in all patients with lupus anticoagulants, that the presence of antiphospholipid antibodies in patients with lupus anticoagulants does not increase the risk of thrombosis in these patients, and that drug-related antibodies are associated with an increased risk of thrombosis. Lupus anticoagulants and antiphospholipid antibodies seem to define two distinct but related patient populations, each associated with an increased risk of thrombosis.