Heterophilic antibodies against rabbit serum causing falsely elevated gonadotropin levels.

Two cases are presented in which previously acquired antibodies against rabbits in the patient's serum caused falsely elevated hormonal levels in radio-immuno assays (RIA) based on rabbit antibodies to follicle-stimulating hormone (FSH) and human chorionic gonadotropin (hCG). The erroneous results led to unnecessary operative intervention and inconvenience for the patients.