What the calcitonin test shows
Calcitonin is a 32-amino-acid hormone from the thyroid’s parafollicular C-cells — a scattered population separate from the follicular cells that make thyroid hormone. Its textbook job, per StatPearls, is to lower blood calcium by curbing osteoclasts (the cells that break down bone). In humans that role is minor — calcium stays normal even when calcitonin is very high.
What makes the test useful is different. Calcitonin is the blood marker for medullary thyroid carcinoma (MTC), a cancer of those same C-cells; MedlinePlus frames it as a test used mainly to diagnose and monitor that cancer.
This sets calcitonin apart from its neighbors on a thyroid panel. TSH, free T4 and free T3 track thyroid function and can be normal while calcitonin is sky-high. Thyroglobulin is also a tumor marker, but for a different disease — differentiated (papillary and follicular) thyroid cancer. The two are complementary, not interchangeable.
Calcitonin normal range
Calcitonin is reported in pg/mL, numerically identical to the SI unit ng/L (1 pg/mL = 1 ng/L), so US and European reports read the same. Basal (resting) values are low, and men run higher than women — they carry roughly twice the C-cell mass. Modern immunoassays give orientation limits like these:
| Group | Orientation upper limit, pg/mL (= ng/L) |
|---|---|
| Women (adult) | up to ~5 |
| Men (adult) | up to ~8.5–10 |
| Children and infants | higher — use an age-specific range |
Two bands matter more than the “normal” cutoff. A basal calcitonin above about 100 pg/mL with a thyroid nodule carries a very high risk of medullary thyroid cancer, while values in the 10–100 pg/mL borderline zone are more often benign and are usually clarified with a calcium stimulation test. Because assays and cut-offs differ between labs, reference ranges depend on the lab, sex and age — always read your result against your own report.
Why calcitonin is high
A raised calcitonin is not the same as cancer — most mild elevations are benign — but it is the finding the test exists to catch, roughly in this order of frequency:
- Benign, non-tumor causes (commonest for mild rises). Chronic kidney disease lifts calcitonin in up to a third of dialysis patients; proton-pump inhibitors and other causes of high gastrin, autoimmune (Hashimoto’s) thyroiditis, a high blood calcium and smoking also nudge it up, as can lab artifacts such as heterophile antibodies.
- C-cell hyperplasia — an overgrowth of C-cells that can precede medullary cancer, especially in hereditary disease.
- Medullary thyroid carcinoma (MTC). StatPearls puts MTC at 1–5% of thyroid cancers, from the C-cells; calcitonin diagnoses it, gauges tumor bulk and tracks recurrence. About a quarter of cases are hereditary (multiple endocrine neoplasia type 2, from RET mutations), so a genuinely high value prompts genetic counseling.
- Other neuroendocrine tumors. C-cells also live outside the thyroid, so tumors of the lung, thymus or pancreas can secrete it.
When is it urgent? A basal value above roughly 100 pg/mL, or any clear rise with a thyroid nodule or a family history of MTC or MEN2, needs prompt specialist assessment — MTC is treated surgically and does better caught early.
Why calcitonin is low
A low or undetectable calcitonin is the reassuring result. There is no “calcitonin deficiency” disease: the hormone plays only a bystander role in human calcium balance, so having little of it causes no symptoms, and people are well with none after the thyroid is removed.
Low calcitonin matters in one situation — follow-up after treatment for medullary thyroid cancer. Here an undetectable level is the target, showing no C-cell tumor tissue remains, while a value that climbs over successive tests is the earliest sign of recurrence. One caveat: a small minority of MTCs make little or no calcitonin (“calcitonin-negative” tumors) and are tracked with carcinoembryonic antigen (CEA) instead.
What to test alongside
Calcitonin is read next to the rest of the thyroid work-up and a couple of cross-checks:
- TSH — the first thyroid test in any nodule work-up; it measures gland function, which calcitonin does not.
- Free T4 and free T3 — thyroid-hormone levels, usually normal despite a raised calcitonin.
- Thyroglobulin — the parallel tumor marker for differentiated thyroid cancer.
- TPO antibodies — flag chronic autoimmune thyroiditis, one benign reason calcitonin drifts up.
- Creatinine — kidney function, since poor clearance is a common cause of a mild rise.
- Vitamin D — part of the wider calcium-regulating picture with calcitonin and PTH.
Also ordered in specialist care (no page here): CEA, which tracks MTC alongside calcitonin, and calcium, whose rise triggers C-cell release.
What to do about an abnormal result
- Don’t panic over a mild rise, and don’t self-diagnose. Most small elevations are benign, and one value is never the whole story.
- Repeat on the same assay. Recheck an abnormal result, and review contributors such as a proton-pump inhibitor with the prescriber (never stop a prescribed drug on your own).
- Match the level to the next step. A borderline value (10–100 pg/mL) is often clarified with a calcium stimulation test; a clearly high value, or any rise with a suspicious nodule, moves straight to imaging and referral.
- See the right doctor. Start with your primary-care physician, who arranges a thyroid ultrasound and refers to an endocrinologist; confirmed MTC is managed by an endocrine surgeon, with RET testing where hereditary disease is possible.
- Follow guideline-based testing. The American Thyroid Association neither recommends nor discourages checking calcitonin in every nodule, but advises it when ultrasound or biopsy is suspicious, or with a personal or family history of MTC or MEN2.
Mini-FAQ
Is calcitonin the same as a calcium test?
No. Calcitonin is a hormone made by thyroid C-cells, while a calcium test measures the mineral itself. In people calcitonin has little effect on blood calcium, so it is used mainly as a tumor marker for medullary thyroid cancer rather than to assess calcium balance.
What does a high calcitonin mean?
Most mild rises are benign — kidney disease, proton-pump-inhibitor use, autoimmune thyroiditis or smoking. A clearly raised level, especially above about 100 pg/mL with a thyroid nodule, points to medullary thyroid cancer and needs prompt specialist review.
Is a low or undetectable calcitonin a problem?
No. There is no calcitonin-deficiency disease, and people stay well with none after the thyroid is removed. In someone treated for medullary thyroid cancer an undetectable calcitonin is the goal, because it signals no tumor tissue remains.
How is calcitonin different from thyroglobulin?
Both are thyroid tumor markers, but for different cancers. Thyroglobulin tracks differentiated (papillary and follicular) thyroid cancer from the gland’s follicular cells; calcitonin tracks medullary thyroid cancer from the C-cells. They are used separately, not interchangeably.
Should everyone with a thyroid nodule have calcitonin measured?
Guidelines differ. The American Thyroid Association neither recommends nor discourages routine testing, but advises it when ultrasound or biopsy findings are suspicious, or when there is a personal or family history of medullary thyroid cancer or MEN2.
