Calcitonin Test: Normal Levels & High Results

What Is Calcitonin?

Calcitonin is a hormone produced by the parafollicular C-cells of the thyroid gland. It helps regulate calcium and phosphate levels in the blood, primarily by inhibiting bone resorption. In my clinical practice, I often request this test when there is a suspicion of medullary thyroid carcinoma (MTC) or to monitor patients with known MTC.

Why Is the Calcitonin Test Ordered?

The calcitonin test is most commonly used to:

• Diagnose medullary thyroid carcinoma (MTC)
• Screen family members for multiple endocrine neoplasia type 2 (MEN2)
• Monitor treatment response in MTC patients
• Detect recurrence of MTC after surgery
• Investigate thyroid nodules with suspicious ultrasound features

Normal Reference Ranges for Calcitonin

Reference ranges can vary by laboratory and assay method. The table below shows typical values I use in my NHS practice. Always compare to your lab's specific normal range.

Note: Some labs report in ng/L (1 pg/mL = 1 ng/L). Elevated levels >100 pg/mL basal are highly suspicious for MTC.

Interpreting High Calcitonin Levels

Is a high calcitonin level dangerous?

Yes, persistently elevated calcitonin often signals medullary thyroid carcinoma, a potentially aggressive thyroid cancer. Elevations above 100 pg/mL (basal) have a high specificity for MTC. However, mild elevations (10–50 pg/mL) can occur in other conditions:

• Renal failure
• Hypergastrinemia (e.g., proton pump inhibitor use)
• Neuroendocrine tumors (e.g., lung carcinoid)
• Pregnancy (physiological rise)
• Heterophilic antibody interference

What can cause a falsely high calcitonin?

I've seen patients worried about mildly elevated values that turned out to be due to kidney disease or even certain medications. Always correlate with clinical context and repeat testing if borderline.

Calcitonin and Medullary Thyroid Carcinoma (MTC)

MTC is a rare thyroid cancer that originates from C-cells. Calcitonin is a highly sensitive tumor marker. Pre-operative levels correlate with tumor burden, and post-operative levels should fall to undetectable if all cancer is removed. Rising calcitonin after surgery suggests recurrence or metastasis.

My patients with MEN2 syndrome (RET mutation carriers) undergo prophylactic thyroidectomy in childhood; calcitonin screening guides surgical timing.

Calcitonin During Pregnancy

Calcitonin levels physiologically increase during pregnancy due to placental production and changes in calcium metabolism. Mild elevations (up to 2-3 times the non-pregnant upper limit) are normal. No specific pregnancy reference ranges exist, so clinicians interpret values cautiously.

How Is the Test Performed?

A standard blood draw from a vein in your arm. Fasting is usually not required, but some protocols recommend fasting and avoiding calcium-rich meals beforehand. Your doctor may order a ‘stimulated’ calcitonin test using intravenous calcium or pentagastrin to increase diagnostic sensitivity—this is done in specialist centres.

Limitations of the Calcitonin Test

• Assay variability between laboratories
• Interference from biotin supplements
• Non-specific mild elevations in many benign conditions
• Need for confirmatory imaging (ultrasound, biopsy) if MTC is suspected

Final Thoughts

Calcitonin is a powerful, but not perfect, tool for thyroid C-cell pathology. In my experience, a thorough history, family screening, and correlation with imaging give the best results. If your calcitonin is borderline or high, don’t panic—work with your endocrinologist to determine the next steps.