Antibodies to thromboplastin in systemic lupus erythematosus: isotype distribution and clinical significance in a series of 92 patients

Abstract

We determined the prevalence and relationship with clinical manifestations of antibodies to thromboplastin (aTP) in 92 patients with systemic lupus erythematosus (SLE). Thirty-two (35%) patients had aTP: 13 (14%) were positive for IgG aTP, 13 (14%) for IgM aTP, and 6 (7%) for both. Patients with aTP had an increased incidence of thrombosis (p = 0.01), thrombocytopenia (p < 0.001), hemolytic anemia (p < 0.001), and fetal losses (p = 0.03). When the IgG and IgM aTP isotypes were analysed separately, the IgG aTP were found to be associated with thrombosis (p < 0.001), thrombocytopenia (p < 0.001), and fetal losses (p = 0.02). The IgM aTP were associated with hemolytic anemia (p < 0.001). A correlation was found between the titers of aTP and those of anticardiolipin antibodies, in both IgG (p < 0.01, r = 0.6) and IgM (p < 0.01, r = 0.64) isotypes, and between the titers of IgG aTP and the diluted Russell's viper venom time used to detect the lupus anticoagulant (p < 0.001, r = 0.42). This test is a reliable, reproducible and sensitive assay for the detection of antiphospholipid antibodies, specially in those patients under anticoagulant therapy.