Newly Observed Interference of Oral Biotin with the Free Testosterone Assay in a Woman with Postmenopausal Virilization

A 74-year-old Caucasian female with symptoms of postmenopausal virilization, including alopecia with frontal balding, acne, and moderate hirsutism, was found to have elevated total testosterone levels but normal free testosterone levels while taking 1 to 3 mg of biotin daily. Upon discontinuation of biotin, her free testosterone levels were found to be elevated, which was consistent with her clinical symptoms. This suggested that biotin supplementation interfered with the free testosterone assay, giving falsely low results. The case highlights the need for awareness among clinicians and laboratorians of the potential for biotin interference in hormone assays to prevent misdiagnosis and inappropriate treatment. This is reported to be the first case of biotin interference with the free testosterone assay.