Which laboratory pattern best indicates hypothyroidism?

Which laboratory pattern best indicates hypothyroidism?

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

Answer: (B)

Elevated TSH with a low Free T4 shows primary hypothyroidism. When the thyroid gland can’t produce enough thyroid hormone, the pituitary responds by raising TSH to stimulate the gland, but the circulating Free T4 remains low because the thyroid isn’t producing enough hormone. This contrasts with hyperthyroidism, where low TSH and high Free T4 reflect an overactive thyroid. A normal TSH with low Free T4 isn’t the typical pattern for primary hypothyroidism and can point to other causes, such as non-thyroidal illness or central hypothyroidism where the pituitary doesn’t raise TSH appropriately. An elevated TSH with high Free T4 is uncommon for primary hypothyroidism and might suggest a TSH-secreting pituitary issue or lab interference rather than the usual thyroid failure.

Elevated TSH with a low Free T4 shows primary hypothyroidism. When the thyroid gland can’t produce enough thyroid hormone, the pituitary responds by raising TSH to stimulate the gland, but the circulating Free T4 remains low because the thyroid isn’t producing enough hormone. This contrasts with hyperthyroidism, where low TSH and high Free T4 reflect an overactive thyroid. A normal TSH with low Free T4 isn’t the typical pattern for primary hypothyroidism and can point to other causes, such as non-thyroidal illness or central hypothyroidism where the pituitary doesn’t raise TSH appropriately. An elevated TSH with high Free T4 is uncommon for primary hypothyroidism and might suggest a TSH-secreting pituitary issue or lab interference rather than the usual thyroid failure.