A perimenopausal woman presented with palpitations, hirsutism, and inability to lose weight. Laboratory tests revealed an unusual endocrine hormonal profile including pituitary hormones (TSH, ACTH, and prolactin) below reference intervals and gonadal (testosterone) and adrenal (cortisol) hormones above reference intervals. Ultimately, after a comprehensive workup including a scheduled surgical procedure, abnormal laboratories were determined due to biotin interference. Biotin (vitamin B7) is a water-soluble vitamin and essential cofactor for the metabolism of fatty acids, glucose, and amino acids. The recommended daily intake of biotin for adults is 30 µg/d. Many over-the-counter products, particularly those marketed for hair, skin, and nail growth, contain biotin 100-fold of recommended daily intake. This case is unique due to the abnormalities observed not only in the well-described TSH "sandwich" immunoassay, but also in tests for gonadal steroids, adrenal, and pituitary hormones. Falsely high as well as falsely low results can be ascribed to biotin. Competitive immunoassays (Fig. 1A)- in this case, tests used initially for serum cortisol and testosterone- can demonstrate falsely high results. Interference falsely lowers the immunometric "sandwich" immunoassay (Fig. 1B)-in this case, TSH. Biotin effect on our patient's endocrine testing led to decidedly abnormal findings, unnecessary medical referrals and diagnostic studies, and comprehensible psychological distress. Interference with one immunoassay, TSH, persisted a full 2 weeks after discontinuation of biotin; indeed, some tests demonstrate sensitivity to lesser quantities of biotin. Improved communication between patients, health care providers, and laboratory professionals is required concerning the likelihood of biotin interference with immunoassays.
Keywords: biotin interference; cortisol; immunoassay; testosterone; thyroid stimulating hormone.