Calcitonin

Sample Type: Serum

Overview:
Calcitonin is a hormone produced primarily by the parafollicular cells (C cells) of the thyroid gland. It plays a key role in calcium homeostasis by lowering blood calcium levels when they are elevated. It achieves this mainly by inhibiting osteoclast activity in bones, which reduces bone resorption and promotes calcium deposition into the bone.

Clinical Significance:
Measurement of serum calcitonin is primarily used as a diagnostic and monitoring tool in medullary thyroid carcinoma (MTC), a type of thyroid cancer arising from C cells that produce calcitonin. Elevated calcitonin levels can indicate the presence of MTC or C cell hyperplasia.

Calcitonin testing is also sometimes used to evaluate disorders of calcium metabolism, such as hypercalcemia or Paget’s disease, but these are less common indications.

Testing Procedure:
The test requires a blood sample collected from the patient’s vein (serum). Calcitonin levels can be measured by immunoassay techniques. Sometimes, a stimulation test using agents like pentagastrin or calcium may be performed to provoke calcitonin secretion and improve diagnostic accuracy.

Interpretation:

Normal Levels: Typically low or undetectable in healthy individuals.

Elevated Levels: May indicate medullary thyroid carcinoma, C cell hyperplasia, or less commonly, other neuroendocrine tumors. Elevated calcitonin can occasionally be seen in renal failure, autoimmune thyroiditis, or other conditions.

Limitations:
Calcitonin is specific for C-cell activity but must be interpreted alongside clinical findings and imaging studies. False positives and negatives can occur, so it is not a stand-alone diagnostic tool.

Summary:
Serum calcitonin testing is a valuable biomarker for medullary thyroid carcinoma diagnosis and monitoring, helping guide treatment decisions and prognosis. It also reflects calcium metabolism related to bone health.