Medical Council of Canada Qualifying Examination (MCCQE) I Practice Test

In primary hypothyroidism, the thyroid gland itself is failing, so overall thyroid hormone production falls. The pituitary senses the low thyroid hormone and increases TSH in an attempt to stimulate the thyroid, but the gland can’t respond adequately. The result is an elevated TSH with a low Free T4 level—the classic pattern for primary hypothyroidism.

If both TSH and Free T4 were normal, you’d be in the euthyroid range. If TSH were low and Free T4 high, that points to hyperthyroidism. An elevated TSH with an elevated Free T4 is not typical for primary hypothyroidism and would raise questions about other causes or assay issues.