Abstract
BACKGROUND The interference of biotin administration with thyroid function tests has been reported; however, it remains unclear in clinical practice. In this report, we present the case of a neonate with a diagnosis of pontocerebellar hypoplasia type 6 (PCH6) treated with biotin who developed biotin interference with laboratory thyroid function tests. CASE REPORT A 1-day-old male infant with hypothermia, tachypnea, and lactic acidosis had a suspected diagnosis of mitochondrial disease. Biotin and several vitamins were administered to improve his condition. On day 14, his laboratory tests revealed a free triiodothyronine level of 4.7 pg/mL, free thyroxine level of 3.7 ng/dL, thyroid-stimulating hormone level of 0.07 μIU/mL, and thyroid-stimulating hormone receptor antibody (TRAb) level of 37.6 IU/L, suggesting Graves' disease. No goiter or tachycardia developed. The maternal thyroid function was not measured during pregnancy, while the maternal TRAb was negative on the same day. After methimazole administration, the patient's thyroid function normalized, and methimazole was therefore discontinued. All thyroid function tests were conducted using immunoassay methods with avidin and biotin. Later, reduced oxygen consumption under aerobic conditions in skin fibroblasts and compound heterozygous variants of the mitochondrial arginine tRNA synthetase gene were identified, and the patient was diagnosed with PCH6. CONCLUSIONS In this case, the clinical symptoms and physical findings were incompatible with the thyroid function. These laboratory findings could have mimicked Graves' disease due to the biotin interference with immunoassays. Therefore, caution is required when evaluating similar cases.