In primary hypothyroidism, what pattern is typically seen in TSH and free T4?

• A. Elevated TSH with low free T4
• B. Low TSH with high free T4
• C. Elevated TSH with high free T4
• D. Normal TSH and free T4

Answer: (A)

In primary hypothyroidism, the problem lies in the thyroid gland itself, so it can’t produce enough thyroid hormone. The drop in circulating free T4 signals the pituitary to ramp up TSH in an attempt to stimulate the thyroid. Since the thyroid isn’t responding adequately, free T4 remains low despite the high TSH. That combination—high TSH with low free T4—is the classic lab pattern for primary hypothyroidism. This differs from other scenarios: if the pituitary isn’t driving TSH (secondary hypothyroidism), TSH may be low or inappropriately normal with low T4; in hyperthyroidism, TSH is suppressed and free T4 is elevated. A pattern of high TSH with normal free T4 can indicate subclinical hypothyroidism.