Heterophilic antibodies interfering with radioimmunoassay. A false-positive pregnancy test.

A young man with amenorrhea had a consistently positive pregnancy test result (serum radioimmunoassay measurement of beta-human chorionic gonadotropin hormone). No fetal or placental tissue was found after uterine curettage and exploratory laparotomy. The false-positive pregnancy test result was due to heterophilic antibovine and antigoat antibodies in the patient's serum. These antibodies interfered with radioimmunoassays using goat antibodies. This case shows that serum heterophilic antibodies can interfere with immunoassays and result in unnecessary diagnostic procedures and/or unnecessary treatment.