Calcitonin Test: Medullary Thyroid Cancer Marker

What Is Calcitonin (CT)?

Calcitonin is a hormone produced primarily by the parafollicular C-cells of the thyroid gland. It plays a minor role in calcium and phosphate metabolism, but its clinical importance lies in its role as a highly specific tumour marker for medullary thyroid carcinoma (MTC). In my clinical practice, a suspicious thyroid nodule together with an elevated calcitonin level almost always points toward MTC.

Why Measure Calcitonin?

The calcitonin test is used for:

• Diagnosis and monitoring of medullary thyroid cancer
• Screening family members in hereditary MTC (MEN2 syndromes)
• Detecting residual or recurrent disease after thyroidectomy

Reference Ranges for Calcitonin

Reference intervals vary by laboratory, assay method, and patient demographics. Below are typical values for fasting calcitonin in adults.

Note: Always interpret results according to your lab’s specific reference range. Elevated values require clinical correlation.

What Does a High Calcitonin Level Mean?

A persistently elevated calcitonin is strongly suspicious for medullary thyroid carcinoma. Other causes include:

• Renal failure (decreased clearance)
• Neuroendocrine tumours (e.g., carcinoid, small cell lung cancer)
• Chronic hypergastrinemia (proton pump inhibitors)
• Pregnancy (mild, transient elevation)

Is a Slightly High Calcitonin Dangerous?

A borderline elevation (e.g., 5–10 pg/mL in a woman) may be benign, especially if the result is not reproducible. In my clinic, I always repeat the test with a stimulation assay (calcium or pentagastrin) to confirm. A stimulated calcitonin above 100 pg/mL strongly suggests MTC.

Calcitonin and Thyroid Nodules

Routine calcitonin screening in all thyroid nodules is debated. Many endocrinology guidelines recommend measuring calcitonin in nodules with suspicious ultrasound features (e.g., solid, hypoechoic, irregular margins). Early detection of MTC dramatically improves outcomes.

Calcitonin During Pregnancy

Pregnancy can cause a mild rise in calcitonin due to placental C-cell activity. Levels usually return to normal after delivery. If a woman of childbearing age presents with an elevated calcitonin, a pregnancy test is prudent before pursuing extensive workup.

Can Medications Affect Calcitonin Levels?

Yes. Proton pump inhibitors (e.g., omeprazole) and other drugs that raise gastrin can increase calcitonin. Always disclose all medications and supplements when having this test.

How Is the Test Performed?

A simple blood draw from a vein, typically after an overnight fast. For stimulation testing, a calcium infusion is given over 10 minutes and blood is drawn at multiple time points. The patient may experience transient warmth or flushing during infusion.

When to See a Doctor

If you have a family history of MEN2 or MTC, or if a routine blood test shows an unexplained elevated calcitonin, schedule an appointment with an endocrinologist. A thyroid ultrasound and fine‑needle aspiration are often the next steps.