Here's a case report where a woman's blood test results were confused by her use of Vitamin B7, or biotin. Since a number of guys on this forum supplement, I thought it was worth mentioning. The abstract says:
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, 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 labs were determined due to biotin interference. Biotin (Vitamin B7) is a water-soluble vitamin and essential co-factor for the metabolism of fatty acids, glucose, and amino acids. The recommended daily intake (RDI) of biotin for adults is 30 µg/day. Many over-the-counter products particularly those marketed for hair, skin, and nail growth, contain biotin 100-fold of RDI. Falsely high as well as falsely low results can be ascribed to biotin. 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 two weeks after discontinuation of biotin; indeed, some tests demonstrate sensitivity to lesser quantities of biotin.