A 55-year-old overweight female patient with elevated parathyroid hormone (PTH) levels, without any other major plasma biochemical abnormalities, and with normal vitamin D and calcium levels. The condition was suggestive of normocalcemic primary hyperparathyroidism. Bone densitometry and 24-hour calciuria were normal. After extensive investigation and possible referral for exploratory surgery, the patient reported continued and chronic use of biotin supplementation (2.5 mg per day). Repeated tests after discontinuing the use of vitamin B7 showed normal PTH levels without surgical or pharmacological interventions. Biotin supplementation associated with the use of this vitamin as a component of biological assays for hormone dosage can generate incorrect laboratory results, which puts medical conduct at risk with inaccurate diagnoses and unnecessary procedures. Although, different substances or emotional conditions can interfere with hormone dosages, one must consider the use of food supplements such as biotin since it can also generate unreliable results. Discontinuation of the use of biotin, in addition to the assessment of serum biotin levels prior to hormone dosing is necessary for a correct evaluation of serum PTH levels. This study was analyzed and approved by the Research Ethics Committee, and obtaining the Informed Consent Form according to CNS/CONEP Resolution 466/12.
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