Calcitonin: The Lab That Watches for Medullary Thyroid Cancer
Written by John P. Sabra, MD FACS
Updated September 2026
Educational only. This article is not medical advice. Always consult your physician about your individual situation.
Calcitonin is a hormone made by the parafollicular C cells of the thyroid, the same cells that medullary thyroid cancer arises from. In a healthy adult, calcitonin does very little for calcium regulation. As a clinical test, though, it is the single most important tumor marker for medullary thyroid cancer, used for diagnosis, post-operative surveillance, and tracking disease activity over time.
Normal serum calcitonin is low, typically under 10 pg/mL in women and under 20 pg/mL in men on modern assays. Levels run higher in men and in patients with kidney disease. An elevated calcitonin in a patient who also has a thyroid nodule is strongly suggestive of medullary thyroid cancer.
Calcitonin is not checked in every patient with a thyroid nodule. Whether routine screening should be done is debated, and published guidelines vary on the point. In most U.S. practice, calcitonin gets checked when there is specific clinical suspicion for medullary cancer.
When Calcitonin Is Measured
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Family history of medullary thyroid cancer or MEN2: A standard part of the workup in this population.
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Thyroid nodule with suspicious features for medullary cancer on biopsy: When the cytology points toward MTC rather than papillary cancer.
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RET mutation carrier: Used to track disease before and after prophylactic thyroidectomy.
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Post-operative surveillance for known medullary thyroid cancer: The primary surveillance marker.
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Unexplained chronic diarrhea with a thyroid finding: Medullary cancer can produce diarrhea through humoral effects.
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Pheochromocytoma diagnosis: Always check, because of the MEN2 association.
⚕ Clinical note A mildly elevated calcitonin is not always cancer. C-cell hyperplasia, certain medications including proton pump inhibitors, chronic kidney disease, and lung disease can all raise calcitonin. A patient with a mildly elevated level needs a careful workup, often including a stimulated calcitonin test, to sort out which of these is responsible.
Interpreting the Number
| Calcitonin Level | Approximate Suspicion |
|---|---|
| Under 10 pg/mL (women), under 20 (men) | Normal. No suggestion of medullary cancer. |
| 10 to 100 pg/mL | Mildly elevated. Further evaluation needed; could be C-cell hyperplasia or small medullary cancer. |
| 100 to 500 pg/mL | Strongly suggestive of medullary thyroid cancer with a discrete tumor. |
| Over 500 pg/mL | Medullary thyroid cancer almost certain; often with lymph node involvement. |
Post-Operative Surveillance
After surgery for medullary thyroid cancer, calcitonin is the primary surveillance marker. In a patient who has been cured, calcitonin should fall to undetectable levels within 2 to 3 months of surgery. A calcitonin that stays elevated after surgery means residual disease somewhere in the body. A calcitonin that rises during follow-up means recurrent disease.
The doubling time of calcitonin is one of the most important prognostic markers I have. A slow doubling time, measured in years, suggests indolent disease that can often be managed with surveillance. A short doubling time, measured in months, suggests aggressive disease and prompts evaluation for systemic therapy.
⚕ Clinical note Calcitonin must be drawn after a fast and processed promptly. The hormone is unstable and degrades if the sample sits at room temperature. Make sure your lab handles it correctly: for most assays it should be drawn on ice and processed within 30 minutes. A poorly handled sample can produce a falsely low value, which is the kind of error that quietly undermines surveillance.
Stimulated Calcitonin Testing
In ambiguous cases, meaning a mildly elevated baseline calcitonin without an obvious tumor, a stimulated calcitonin test may be performed. Pentagastrin used to be the standard stimulus, but it is no longer available in the United States. Calcium-stimulated testing has largely replaced it. The test measures how much calcitonin rises in response to a stimulus, which helps distinguish C-cell hyperplasia from medullary cancer.
The Bottom Line
Calcitonin is the most useful tumor marker for medullary thyroid cancer. It is used for diagnosis, post-operative surveillance, and tracking disease over time. Interpreted in clinical context, the level separates normal from mildly elevated, which is often C-cell hyperplasia, from clearly elevated, which suggests medullary cancer. It is not used routinely for all thyroid nodules, but it is essential when MTC is suspected or being followed.
If you have a family history of medullary thyroid cancer, or you have been told your calcitonin is elevated, make sure the workup includes ultrasound, careful sample handling, and evaluation by an endocrinologist familiar with medullary thyroid cancer.
This article is intended for patient education only. It does not constitute medical advice and does not replace a consultation with your physician. Individual patient circumstances and clinical judgment determine the appropriate evaluation and management for every patient.
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