A patient with fatigue, cold intolerance, and constipation has a low free T4 and elevated TSH. What is the diagnosis?

• A. Subclinical hypothyroidism
• B. Overt primary hypothyroidism
• C. Central hypothyroidism
• D. Hyperthyroidism

Answer: (B)

The key idea is how TSH and free T4 levels distinguish where the problem lies in thyroid function. In primary hypothyroidism, the thyroid gland itself fails to produce enough hormone, so free T4 is low and the pituitary responds by raising TSH. In central (secondary/tertiary) hypothyroidism, the pituitary or hypothalamus isn’t driving TSH properly, so TSH is low or inappropriately normal even if T4 is low. Subclinical hypothyroidism would show a high TSH with a normal free T4, and hyperthyroidism would show a high free T4 with a suppressed TSH.

Here, the patient’s fatigue, cold intolerance, and constipation align with hypothyroidism. The labs show a low free T4 together with an elevated TSH, indicating that the thyroid gland is underactive and the pituitary is attempting to stimulate it. This pattern is overt primary hypothyroidism, where clinical symptoms accompany biochemical evidence of both low thyroid hormone and high TSH.