Calcitonin is a hormone produced by special cells in the thyroid called C-cells. Calcitonin is involved in the regulation of calcium levels in the blood and inhibits bone breakdown (resorption). A calcitonin test provides additional information if there are symptoms of medullary thyroid cancer or a family history of this condition. Calcitonin also appears to be a valuable aid in the management of certain types of osteoporosis. An 8 to 12 hour fast is required for this blood test. However, drink plenty of water and take medications as prescribed.