Fellow Sparrow Hospital/MSU Lansing, Michigan, United States
Introduction : Biotin is a water-soluble vitamin necessary for metabolism of fatty acids, glucose, and amino acids to be used as energy for the body. Recommended daily intake of biotin for adults is up to 100 mcg daily. Daily multivitamins contain biotin doses of about 30 mcg. Hair, skin, nail vitamins can have doses reaching up to 10,000 mcg. There is an established association of biotin with thyroid hormone measurements leading to false elevations of free T4 and free T3 and low levels of thyroid stimulating hormone. The American Thyroid Association recommends holding biotin at least 2 days prior to lab testing to avoid this potential interaction. Here we present a case of a patient being treated for Graves’ disease who developed new thyroid laboratory abnormalities while on biotin.
Case(s) Description : The patient is a 35 year old female who was referred for abnormal thyroid labs and hyperthyroid symptoms. She was diagnosed with Graves’ disease and started on treatment. She was then seen as a routine follow-up visit where she was noted to have improvement in many of her initial presenting symptoms but had noticed more hair loss. She was maintained on methimazole and propranolol. Her last set of labs two months prior to office visit showed TSH 0.34 uIU/mL (0.35-4.01) with FT4 0.75 NG/dL (0.61-1.37) and FT3 4.4 pg/mL (2.8-4.4). She had lab studies done after the visit which showed a TSH 1.86 uIU/mL with elevated FT4 and FT3 of 1.43 NG/dL and 6.4 pg/mL respectively. After thinking of how the patient could have worsening thyroid dysfunction despite taking her medications as prescribed we recalled that she had mentioned hair thinning and she was called to see if she was on biotin which she confirmed she was taking at the time of the labs. She was asked to hold biotin and repeat labs. Five days later laboratory studies showed TSH 1.13 uIU/mL, FT4 0.88 NG/dL and FT3 4.1 pg/mL. At this time her methimazole dose was adjusted and repeat labs pending.
Discussion : Biotin interference with thyroid immunoassays occurs due to the biochemical properties of biotin with its strong bonding with streptavidin which allows for detection at lower concentrations. The Streptavidin-biotin binding is used in assays in two categories: competitively and in a sandwich method. The competitive assay measures smaller molecules like T3 and T4 and the sandwich method measures TSH. With the competitive method, excess biotin prevents binding of the T3 or T4 analyte to the streptavidin site which is then removed during a wash step. The serum concentration of the analyte is inversely related to the signal intensity, which leads to falsely elevated levels. In the sandwich method as the assay signal is directly related to analyte concentration, excess biotin occupies the streptavidin binding sites preventing the binding of TSH leading to falsely low levels. Not being aware of this interaction could lead to a false new diagnosis of hyperthyroidism, dosage adjustment for patients being treated for Graves’ or dose decrease in patients with hypothyroidism. This case highlights the importance of awareness of thyroid lab interferences and to routinely ask patients about over the counter supplement use to prevent potential mistreatment for the patient.
