Calcitonin tests measure the level of calcitonin — a hormone produced by the parafollicular C‑cells of the thyroid — in the blood. Clinically, they are used as a tumor marker because markedly elevated calcitonin is highly suggestive of medullary thyroid carcinoma (MTC) and can aid in screening, diagnosis, staging, and monitoring for recurrence or treatment response.

Results must be interpreted with caution: borderline or mildly elevated levels can occur with C‑cell hyperplasia, other neuroendocrine tumors, renal failure, certain medications (e.g., proton pump inhibitors), smoking, or inflammation. Stimulated tests (calcium or pentagastrin) may be used to uncover occult disease when basal levels are equivocal, but rising or very high calcitonin concentrations are the strongest indicators of MTC.

Your calcitonin level is measured from a blood sample drawn by a healthcare professional (venipuncture). The phlebotomist collects blood into the appropriate tube, the laboratory separates serum or plasma, and the sample is analyzed for calcitonin concentration.

Most routine tests require just a single fasting or non‑fasting blood draw depending on the lab’s instructions; for unclear or borderline results a clinician may order a stimulation test (usually an IV calcium or historically pentagastrin challenge) with multiple timed blood draws to see how calcitonin responds. Always follow the specific prep instructions you’re given and tell the provider or lab about any medications, supplements, or smoking, since these can affect results.

Calcitonin is a hormone produced by thyroid C‑cells; blood calcitonin is used primarily as a marker of C‑cell activity and is most helpful for identifying or monitoring medullary thyroid carcinoma (MTC). A clearly elevated result raises the possibility of C‑cell hyperplasia or MTC and usually prompts repeat testing and further evaluation (imaging, possible stimulation testing, and referral to an endocrinologist or thyroid specialist). After treatment for MTC, falling or undetectable calcitonin usually indicates good response, while rising levels suggest persistent or recurrent disease.

Normal or low calcitonin makes active MTC less likely but does not absolutely rule out very small tumors or rare cases; test interpretation depends on the assay, lab reference ranges (which differ by sex), and clinical context. Mild elevations can occur for non‑cancer reasons—chronic kidney disease, smoking, certain neuroendocrine tumors, inflammation, and some medications—so isolated borderline increases often lead to repeat testing, consideration of a stimulation test, and investigation of other causes rather than immediate diagnosis. Always review your specific result, the lab reference range, and next steps with your clinician who can correlate calcitonin with imaging, family history, and genetic testing (eg, RET) when appropriate.

Calcitonin testing is a useful but not infallible marker for medullary thyroid carcinoma (MTC): elevated levels are strongly suggestive of C‑cell disease and are highly sensitive for clinically relevant MTC, but low or borderline values do not absolutely exclude very small tumors. False positives can occur because calcitonin rises with other conditions (C‑cell hyperplasia, renal failure, certain medications, smoking, and some inflammatory states), and false negatives can occur with very small lesions or with assay limitations.

Interpretation depends on the assay, sex-specific reference ranges, and the trend over time: absolute levels, reproducible increases, and calcitonin doubling time are more informative than a single borderline result. Stimulation tests (historically pentagastrin, now sometimes calcium) can increase sensitivity but are not universally available and can reduce specificity. Because assays vary between labs, calcitonin results should be interpreted alongside clinical findings, imaging, and specialist input rather than used alone to make definitive cancer diagnoses.

How often you should test calcitonin depends on the reason: routine screening of the general population is not recommended, but testing is used when medullary thyroid carcinoma (MTC) is suspected, when calcitonin was previously elevated, or for follow‑up after MTC treatment.

Typical schedules used by clinicians are: at diagnosis and then every 3–6 months in the first 1–2 years after surgery, moving to every 6–12 months long‑term if levels are stable; for people with RET gene mutations the timing is individualized but many centers perform periodic (often annual) measurements starting in childhood or adolescence depending on mutation risk. Follow the schedule your endocrinologist or surgeon recommends for your specific situation.

No — calcitonin test results are not by themselves diagnostic of cancer; they indicate patterns of imbalance or resilience in calcitonin levels that can raise suspicion but do not constitute a definitive medical diagnosis.

Calcitonin results must be interpreted by a qualified clinician alongside symptoms, clinical history, imaging, and other laboratory or biomarker data to determine whether further diagnostic workup or treatment is required.

Calcitonin is mainly used as a marker for medullary thyroid carcinoma (MTC), so an elevated result should prompt clinical follow‑up rather than self‑directed attempts to “fix” the number. The usual steps are repeat and confirm the value (same assay), have an endocrinologist review it, and investigate noncancer causes (for example chronic kidney disease, other neuroendocrine tumors, certain medications and smoking can raise levels). Definitive lowering of calcitonin depends on treating the underlying cause—for MTC this may require surgery and specialist oncologic/endocrine management; for noncancer causes it means treating or removing the contributing condition.

Practical actions you or your clinician may take include repeating the test, reviewing and possibly stopping medications that could affect results, quitting smoking, assessing kidney function, and considering genetic testing for RET mutations or imaging if MTC is suspected. Work with an endocrinologist or endocrine surgeon to get a tailored plan—only targeted medical or surgical treatment of the underlying diagnosis will reliably reduce calcitonin levels.