Serum calcitonin is normally produced by the C cells of the thyroid. It functions to reduce serum calcium by inhibiting release of calcium from bone. It is a peptide with a molecular weight of 3400, and has a half life of approximately 12 minutes. It is characteristically elevated in medullary carcinoma of the thyroid. Since medullary carcinoma often occurs as an autosomal disorder, family members of patients with this condition should be screened for serum calcitonin.

Serum calcitonin is typically elevated in which of the following conditions: