Calcitonin Blood Test: High Levels & Thyroid Cancer

The calcitonin blood test is the key tumor marker for medullary thyroid cancer. Learn normal levels, what high calcitonin means, and the benign causes (kidneys, PPIs, smoking) behind it.

Published July 20, 202610 min readWritten by the Blood Analysis Team · Reviewed and verified by Julien Priour

Calcitonin is a hormone made by the C cells of the thyroid gland. Its role in calcium balance is minor in humans, but the calcitonin blood test has one very specific job: it is the key tumor marker for medullary thyroid cancer (MTC), a rare thyroid tumor. This guide covers normal calcitonin levels, what a high result means, why a modestly elevated value is not the same as cancer, and how the test is used for screening (families carrying a RET gene mutation) and follow-up. Calcitonin is part of evaluating the gland — see also the thyroid panel.

Key takeaways

Calcitonin is a hormone made by the thyroid's C cells; its clinical value is not calcium but medullary thyroid cancer (MTC), for which it is the key tumor marker.¹²
Indicative low baseline values: often < ~10 pg/mL in men and < ~5 pg/mL in women, depending on the lab, the assay, and sex.²³
Calcitonin level tracks tumor burden: the higher it is, the larger the tumor or the more extensive the spread; a markedly high value (> 100 pg/mL, and especially > 500) is strongly suggestive.¹⁴
Many modest elevations are not cancer: kidney disease, proton pump inhibitors (PPIs), smoking, high calcium, C-cell hyperplasia, other neuroendocrine tumors, pregnancy, and newborns can all raise the number.²⁵
For intermediate values, a stimulation test (with calcium) or a second marker (procalcitonin) helps sort things out.³²
Calcitonin is also used for family screening (RET mutation carriers, MEN2) and for post-operative monitoring of MTC.⁵

What is calcitonin?

Calcitonin is a peptide hormone (32 amino acids) secreted by the thyroid's C cells, also called parafollicular cells. These are different from the follicular cells that make the thyroid hormones T3 and T4 regulated by TSH.¹

Its name comes from its historical action on calcium: calcitonin tends to lower blood calcium by slowing bone breakdown. But in adult humans this role is minor and largely redundant — people can live without a thyroid (and therefore without calcitonin) with no meaningful calcium problem. That is why calcitonin is not a test of calcium metabolism; for that, clinicians measure calcium, vitamin D, and parathyroid hormone instead.

The whole value of the test lies elsewhere: when C cells multiply abnormally (hyperplasia) or turn cancerous (medullary thyroid cancer), they produce much more calcitonin. The blood level then directly mirrors that activity, which is what makes calcitonin an excellent tumor marker.²¹

Calcitonin is not procalcitonin. Don't confuse calcitonin (the thyroid marker measured here) with procalcitonin (PCT), a marker of bacterial infection. They are two different tests, even though procalcitonin can sometimes serve as a supplementary marker for MTC.³

Why the test is done

Calcitonin is not part of a routine panel. Your clinician may order it in three main situations:⁵¹

When you have a thyroid nodule, to avoid missing a medullary thyroid cancer: a high calcitonin points toward MTC, which ultrasound and fine-needle aspiration detect less reliably than other thyroid cancers.⁶
For family screening: MTC is inherited in about a quarter of cases, as part of the multiple endocrine neoplasia type 2 (MEN2) syndromes caused by a mutation in the RET gene. In carriers, calcitonin guides surveillance and the timing of surgery.⁵
For follow-up after surgery for MTC: a calcitonin that becomes undetectable after removal is reassuring, while a calcitonin that rises again signals recurrent or residual disease.⁵⁴

The debate over routine testing. Should calcitonin be measured in every thyroid nodule? Recommendations differ between countries. Some professional societies (notably in Europe) advise it because it catches MTC earlier; others are more cautious, because modest elevations are common and rarely cancerous, with a risk of overdiagnosis and unnecessary work-up.⁶⁵ What is right for you is decided by your clinician, based on your situation.

Do you need to fast?

In general, the calcitonin test does not require strict fasting. It is, however, wise to avoid smoking just before the draw, because tobacco can raise the level and muddy the interpretation. Some labs apply special handling rules (the tube sent quickly, sometimes chilled). Follow the exact instructions on your order (see Do you need to fast before a blood test?).²⁷

Normal ranges

Below are indicative adult reference values for basal (unstimulated) calcitonin. They depend heavily on the lab's assay and on sex (men run slightly higher, because they have more C cells). Always compare against the range printed on your report.

Situation	Basal calcitonin (indicative)	Unit
Women (normal)	< ~5	pg/mL
Men (normal)	< ~10	pg/mL
Intermediate zone (needs work-up)	~10 – 100	pg/mL
Strongly suggestive of MTC	> 100	pg/mL
Metastases likely / staging	> 500	pg/mL

Units: the usual unit is pg/mL (equivalent to ng/L), so U.S. and European results use the same numbers. Thresholds vary widely by assay kit — the same sample can give different figures from one lab to another. A markedly high baseline value tracks closely with tumor burden, whereas intermediate values often call for a stimulation test or a repeat measurement.²⁴³⁸ Only your clinician can interpret the number in your context.

Understanding your results

High calcitonin: causes

A high calcitonin should prompt a search for a cause. Contrary to a common fear, it does not automatically mean "cancer" — especially when the elevation is modest. The causes fall into two broad groups.²⁵

C-cell causes (tumor or pre-tumor):

Medullary thyroid cancer (MTC) — the reason the test exists. The level tracks tumor burden; a markedly high value (> 100 pg/mL, and especially > 500 pg/mL) is strongly suggestive and triggers a full work-up (tumor markers, imaging).¹⁴
C-cell hyperplasia, a benign (but sometimes precursor) overgrowth that modestly raises calcitonin.²

Non-tumor elevations ("false positives" for cancer):

Kidney disease — the kidneys clear calcitonin, so reduced filtration raises it;²
Proton pump inhibitors (PPIs) — very common heartburn medications that stimulate C cells;²
Smoking;
High blood calcium, some forms of thyroiditis, other neuroendocrine tumors (lung, pancreas), and physiologically pregnancy and the newborn period (naturally higher values).²

That is why a mildly high calcitonin is always read with context: the magnitude of the value, its trend, and, when needed, a stimulation test are what point the way — not a single isolated number.

Low or undetectable calcitonin

A low or undetectable calcitonin is the normal, reassuring situation: it means the C cells are working normally. After surgery for medullary thyroid cancer, an undetectable calcitonin is in fact the goal, a sign of complete removal.⁵ A low level needs no treatment.

The stimulation test

For intermediate values (say, between the lab's threshold and ~100 pg/mL), a stimulation test may be done: calcium is injected (pentagastrin was used in the past but is now scarce) and the rise in calcitonin is measured. A very strong response points toward a C-cell disorder; a weak response is reassuring. More recently, a second marker, procalcitonin, is being studied to settle these intermediate cases without an injection.³²

What affects your calcitonin

Several factors change the calcitonin level regardless of any cancer: sex (higher in men), kidney function, PPI use, smoking, blood calcium, some forms of thyroiditis, pregnancy and the newborn period, and the lab's assay (results are not always comparable between labs). Tell your clinician about your medications (especially PPIs) and habits (smoking) — they change the interpretation.²⁵

Recent research

According to recent PubMed-indexed publications:

Calcitonin remains the most reliable MTC marker. A 2023 umbrella review (a systematic review of systematic reviews) confirms that calcitonin is the best-performing diagnostic marker, that ultrasound and cytology are less sensitive for MTC than for other thyroid cancers, and that measuring calcitonin in the needle-washout fluid from a fine-needle aspiration improves the diagnosis of uncertain nodules.⁶
Thresholds that predict outcome. A 2021 study showed that a pre-operative calcitonin above a certain cut-off (≈ 300 pg/mL in that cohort) was the strongest predictor of recurrence, helping tailor follow-up after surgery.⁴
Sorting out intermediate values. A 2025 prospective study proposes a two-step approach combining calcitonin and procalcitonin: with a calcitonin cut-off of > 10 pg/mL, sensitivity reaches ~0.91 and specificity ~0.98, and procalcitonin helps correctly reclassify most cases between 10 and 100 pg/mL, limiting overtreatment.³
Calcitonin and weight-loss/diabetes drugs. GLP-1 receptor agonists (used for diabetes and obesity) carry a warning for people with a personal or family history of MTC or MEN2; the exact role of calcitonin in monitoring them is currently under discussion.⁹

These findings concern diagnosis and research; they do not authorize self-medication and do not replace your physician's advice.

Get your calcitonin interpreted by AI DiagMe

A calcitonin level is never read alone: its meaning depends on the magnitude of the value, your kidney function, your medications (such as PPIs), your smoking status, and the context (a nodule, a family history). That cross-reading is what gives the result its real value.

👉 AI DiagMe interprets your lab results — blood, urine, or stool — in plain language, taking your whole profile into account. An informational service that does not provide a diagnosis and complements, never replaces, your physician.

Frequently asked questions

What is a calcitonin blood test?

It measures calcitonin, a hormone made by the thyroid's C cells. Its calcium role is minor in humans; the test's medical value is as the key tumor marker for medullary thyroid cancer.

What is a normal calcitonin level?

Indicatively < ~5 pg/mL in women and < ~10 pg/mL in men (basal calcitonin), but thresholds vary widely by lab and assay. Read the range printed on your own report.

Does high calcitonin mean cancer?

Not necessarily. A modest elevation often has a benign cause: kidney disease, PPIs, smoking, C-cell hyperplasia, high calcium, pregnancy. It is a markedly high value (especially > 100, and above all > 500 pg/mL), its trend, or a positive stimulation test that point toward medullary thyroid cancer. Only your clinician can conclude.

What should I do if my calcitonin is slightly high?

Don't panic, but discuss it with your clinician. They will look for a simple cause (kidneys, PPIs, smoking), may repeat the test, and if needed order a calcium stimulation test or a thyroid ultrasound. What happens next depends on the whole picture.

Do I need to fast for a calcitonin test?

Strict fasting is usually not required, but avoid smoking just before the draw. Follow your lab's instructions, as it may have special handling rules.

What is calcitonin family screening?

Medullary thyroid cancer is inherited in about a quarter of cases (multiple endocrine neoplasia type 2, a RET gene mutation). In affected families, calcitonin and genetic testing guide surveillance and the timing of any preventive surgery, decided by a specialist.

What's the difference between calcitonin and procalcitonin?

Calcitonin is the thyroid (C-cell) marker measured here. Procalcitonin is mainly a marker of bacterial infection; it is also being studied as a supplementary MTC marker for uncertain cases.

What is calcitonin used for after MTC surgery?

For follow-up. A calcitonin that becomes undetectable is reassuring (complete surgery). A calcitonin that rises over time signals recurrent or residual disease and prompts a work-up.

Bottom line

Calcitonin is a hormone from the thyroid's C cells whose value is not calcium but medullary thyroid cancer (MTC), for which it is the key tumor marker: diagnosis in a nodule, screening of families carrying a RET mutation (MEN2), and follow-up after surgery. Keep in mind that baseline values are low (< ~10 pg/mL men, < ~5 pg/mL women, depending on lab and sex), that a markedly high level tracks tumor burden, but that a modest elevation often has a benign cause (kidneys, PPIs, smoking, high calcium). It is not the isolated number but the context, the trend, and sometimes a stimulation test that matter. No value is read alone — it's your whole set of markers and your context that counts, which is what AI DiagMe provides, alongside your physician.

Sources

Official sources and peer-reviewed publications (PubMed) used for this guide:

Thomas CM, Asa SL, Ezzat S, et al. Diagnosis and pathologic characteristics of medullary thyroid carcinoma — review of current guidelines. Curr Oncol, 2019. PubMed · DOI ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶
Bae YJ, Schaab M, Kratzsch J. Calcitonin as biomarker for the medullary thyroid carcinoma. Recent Results Cancer Res, 2015. PubMed · DOI ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴
Clausi C, Censi S, Zanin E, et al. Combining procalcitonin and calcitonin for the diagnosis of medullary thyroid cancer: a two-step approach. Clin Endocrinol (Oxf), 2025. PubMed · DOI ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶
Park H, Park SY, Park J, et al. Prognostic value of preoperative serum calcitonin levels for predicting the recurrence of medullary thyroid carcinoma. Front Endocrinol (Lausanne), 2021. PubMed · DOI ↩ ↩² ↩³ ↩⁴ ↩⁵
Wells SA, Asa SL, Dralle H, et al. Revised American Thyroid Association guidelines for the management of medullary thyroid carcinoma. Thyroid, 2015. PubMed · DOI ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹
Trimboli P, Mian C, Piccardo A, Treglia G. Diagnostic tests for medullary thyroid carcinoma: an umbrella review. Endocrine, 2023. PubMed · DOI ↩ ↩² ↩³
MedlinePlus (U.S. National Library of Medicine, NIH) — Calcitonin Blood Test. medlineplus.gov ↩
Testing.com — Calcitonin Test. testing.com ↩
Kelly CA, Sipos JA. Approach to the patient with thyroid nodules: considering GLP-1 receptor agonists. J Clin Endocrinol Metab, 2025. PubMed · DOI ↩