Question of the Week
For September 19, 2017
An 8-year-old girl presents with her mother, who states that the girl’s neck seems to have thickened. The girl’s weight has been stable, and she has not had any generalized swelling, heat or cold intolerance, difficulty breathing, or change in bowel or bladder habits.
Her temperature is 36.1°C, her heart rate is 70 beats per minute, and her respiratory rate is 14 breaths per minute. She appears well. Her neck is supple. The thyroid is firm and slightly enlarged; there are no palpable nodules.
Her serum thyroid-stimulating hormone level is 8.5 μU/mL (reference range, 0.6–6.3).
Which one of the following laboratory tests would confirm the diagnosis for this child?