Thyroid Disorders USMLE Step 1 Practice Question
A 23-year-old woman began oral contraceptive pills 6 weeks ago. She reports palpitations and mild heat intolerance but denies weight loss or neck pain. Vital signs show HR 92 bpm, BP 118/76 mmHg, RR 16/min, temperature 37.2°C. Laboratory studies reveal total T4 11.2 ng/dL (normal 4.5-12), free T4 1.2 ng/dL (normal), and TSH 1.8 mIU/L (normal). Thyroid ultrasound shows no nodules. Which mechanism best explains these findings?
Answer choices
- APrimary thyroid gland hyperplasia
- BReduced hypothalamic TRH secretion
- CDecreased activity of type 1 deiodinase
- DIncreased production of thyroxine binding globulinCorrect answer
- EResistance of peripheral tissues to thyroid hormone
- FIncreased conversion of T4 to T3 by peripheral tissues
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