Biotin Supplementation Creates the Misleading Diagnosis of Secondary Adrenal Insufficiency

Introduction: Biotin (vitamin B7) is a water-soluble vitamin and an essential cofactor for the metabolism of fatty acids, glucose, and amino acids. Cases of biotin interference with laboratory testing have been described, most of which involve interference with thyroid function tests. Interference with gonadal steroids, adrenal, and pituitary hormones are rare. We report a case of T3 thyrotoxicosis in which biotin supplementation created the appearance of secondary adrenal insufficiency (AI). Case: A 66-year-old woman was referred for the evaluation of low TSH. She had chronic fatigue, low libido, and dizziness on standing. Vitals were stable with BP 135/64 mmHg and BMI 23.5. No evidence of mucosal or cutaneous hyperpigmentation. Laboratory evaluation revealed low ACTH <5 (7.2–63.3 pg/mL), low morning cortisol 3.8 and high DHEA-S 174 (13–130 ug/dL). TSH was low at 0.32 (0.32–5.60 uIU/mL) with normal prolactin and appropriately elevated FSH and LH. The labs raised concern for secondary AI. Cosyntropin stimulation test (CST) was done with a peak cortisol of 17.4 ug/dL. In the setting of suppressed ACTH and failed CST, she was started on Hydrocortisone therapy. Subsequently, CT of abdomen was obtained due to high DHEA-S which showed normal appearance of both adrenals. Pituitary MRI was normal. A detailed review of the medication list revealed that the patient was taking a Biotin containing multivitamin. Repeat labs 1 week after stopping biotin showed normalization of ACTH 13.8 (7.2–63.3). Repeat CST showed a peak cortisol response of 24 ug/dL. Hydrocortisone was discontinued and the patient remained stable on subsequent follow-ups, without the need for further glucocorticoid replacement therapy. Thyroid lab abnormalities persisted after biotin cessation which led to the diagnosis of T3 thyrotoxicosis, the treatment of which caused resolution of the patient’s symptoms. Discussion: The recommended daily intake of biotin for adults is 30 µg/d. Many over-the-counter products, specifically those marketed for hair, skin, and nail growth, contain biotin 100-fold higher than the recommended intake. Biotin interference with competitive immunoassays can cause falsely elevated hormone levels, whereas biotin interference with immunometric “sandwich” assays falsely lowers hormone levels. In our case, low ACTH was clinically misleading, prompting numerous unnecessary radiographic and laboratory testing and treatment with hydrocortisone. The US Food and Drug Administration issued a safety communication regarding biotin interference with laboratory tests. Education and communication between laboratorians, providers, and patients play an important role in investigating potential lab interference and the need for alternative lab assays for an accurate diagnosis. Patients should be asked to stop taking biotin supplements for at least 48 hours prior to specimen collection if possible.