In primary hypothyroidism, TSH levels are typically high due to feedback. Which option correctly states this relationship?

• A. TSH is low
• B. TSH is typically high due to feedback
• C. TSH is normal
• D. TSH is fluctuating

Answer: (C)

The main idea here is how the hypothalamic-pituitary-thyroid axis works. In primary hypothyroidism, the thyroid gland isn’t producing enough thyroid hormone (T4/T3). Because there’s less circulating thyroid hormone, the negative feedback to the pituitary is reduced, and the pituitary ramps up its output of TSH in an attempt to stimulate the thyroid again. So TSH levels become elevated.

That’s why the statement that TSH is typically high due to feedback is the best description. A low TSH would point toward hyperthyroidism or pituitary failure rather than primary thyroid failure. A normal TSH would suggest a euthyroid state or perhaps subclinical disease, but not the typical pattern of established primary hypothyroidism. Fluctuating TSH isn’t the characteristic pattern you’d expect in a straightforward primary hypothyroid case.