A 40-year-old female is diagnosed with primary hypothyroidism and started on levothyroxine 75 mcg daily. She returns for a follow-up visit. When should her thyroid-stimulating hormone (TSH) level be rechecked to assess the adequacy of treatment?

The correct answer to the question "A 40-year-old female is diagnosed with primary hypothyroidism and started on levothyroxine 75 mcg daily. She returns for a follow-up visit. When should her thyroid-stimulating hormone (TSH) level be rechecked to assess the adequacy of treatment?" is Option B: 6 weeks after starting levothyroxine.

The other options — A) 2 weeks after starting levothyroxine, C) 3 months after starting levothyroxine, D) 6 months after starting levothyroxine — are incorrect for this USMLE Exam Prep question. As explained above: The half-life of levothyroxine is approximately 7 days. It takes about 5-6 half-lives (5-6 weeks) to reach a new steady state in the body. Therefore, TSH should be rechecked around 6 weeks after star…