Hepatitis B antigen and systemic lupus erythematosus. False positive complement fixation due to anti-antibodies

Sera from 22 patients with systemic lupus erythematosus (SLE) were examined for the presence of hepatitis B antigen (HBsAG) by a complement fixation (CF) test, by an immunoelectrophoretic method (counterelectrophoresis-CEP), and by radioimmunoassay (RIA). The sera from 8 patients gave positive results using CF. However, the same sera and sera from 28 additional SLE patients, when tested with CEP and RIA, were not shown to contain HBsAG.