Unit Converter
Calcitonin
(Thyroid C-Cell Hormone – Marker for Medullary Thyroid Carcinoma)
Synonyms
- Calcitonin
- Thyrocalcitonin
- CT
- C-cell hormone
- Hypocalcemic hormone
Units of Measurement
- pmol/L
- pg/mL
- pg/dL
- pg/100 mL
- pg%
- pg/L
- ng/L
Description
Calcitonin is a 32–amino acid peptide hormone produced by the parafollicular C-cells of the thyroid gland.
Its main physiological function is to lower blood calcium levels by:
- Inhibiting osteoclast activity
- Decreasing bone resorption
- Increasing renal calcium excretion
Clinically, calcitonin is a tumor marker for:
- Medullary Thyroid Carcinoma (MTC)
- C-cell hyperplasia
- MEN2A & MEN2B syndromes (RET mutations)
Calcitonin is extremely sensitive for detecting MTC - often elevated years before symptoms.
Physiological Role
- Lowers serum calcium (opposes PTH action)
- Suppresses osteoclasts
- Minor role in normal calcium homeostasis in adults
- More significant in childhood & pregnancy
Main clinical utility is as a tumor marker, not a calcium-regulating hormone.
Clinical Significance
Elevated Calcitonin
1. Medullary Thyroid Carcinoma (Most Important)
- Diagnostic
- Prognostic
- Used for follow-up
Interpretation: - >100 pg/mL → high suspicion for MTC
- >500 pg/mL → metastatic disease likely
2. C-Cell Hyperplasia
Pre-malignant condition, especially in families with RET mutations.
3. MEN2 Syndromes
- MEN2A
- MEN2B
- FMTC (Familial Medullary Thyroid Carcinoma)
4. Neuroendocrine Tumors
- Pancreatic NETs
- Lung carcinoids
- Small cell lung cancer
5. Chronic Kidney Disease
Reduced clearance → mild elevation.
6. Drugs
- Proton pump inhibitors (PPI)
- β-agonists
- Calcium infusion
- Glucagon stimulation
Low Calcitonin
Not clinically significant.
(MTC may rarely produce low/normal calcitonin - procalcitonin may help.)
Reference Intervals
(Tietz 8E + ATA Thyroid Cancer Guidelines + Mayo + ARUP)
Adults
Men:
- < 10 pg/mL
- < 2.9 pmol/L
Women:
- < 5 pg/mL
- < 1.5 pmol/L
Suspicious for MTC
- 10–100 pg/mL → repeat test / stimulation test
- > 100 pg/mL → very high suspicion
- > 500 pg/mL → metastatic disease likely
Stimulation Test (when needed)
Calcium or pentagastrin stimulation:
- Normal: < 100 pg/mL
- MTC: exaggerated rise > 200–500+ pg/mL
Unit Meanings
| Unit | Explanation |
| pmol/L | picomole per liter |
| pg/mL | picogram per milliliter |
| pg/dL | picogram per deciliter |
| pg/100 mL | same as pg/dL |
| pg% | pg per 100 mL |
| pg/L | picogram per liter |
| ng/L | nanogram per liter |
Diagnostic Uses
1. Diagnosis of Medullary Thyroid Cancer
Highest sensitivity tumor marker.
2. Postoperative Monitoring
- Calcitonin should become undetectable after total thyroidectomy.
- Persistent elevation → residual disease.
- Rising calcitonin → recurrence.
3. Screening in RET Mutation Carriers
Annual testing recommended.
4. Investigating Thyroid Nodules
Calcitonin >20–30 pg/mL warrants evaluation for MTC.
5. Neuroendocrine Tumor Assessment
Calcitonin elevated in some NETs.
6. Stimulation Testing
When baseline values are equivocal (e.g., borderline elevation).
Analytical Notes
- Measure via immunoassay (chemiluminescence).
- Avoid biotin supplements (may interfere).
- PPIs elevate calcitonin — stop 1 week prior if possible.
- Fasting sample preferred.
- Hemolysis minimal impact.
Clinical Pearls
- Calcitonin >100 pg/mL is almost always MTC until proven otherwise.
- If calcitonin is elevated, always check CEA (also rises in MTC).
- RET genetic testing recommended for all confirmed cases of MTC.
- Very high levels (>1000 pg/mL) strongly indicate distant metastases.
- Calcitonin doubling time < 6 months → aggressive tumor behavior.
Interesting Fact
Calcitonin discovery in 1962 initially suggested a major role in calcium metabolism-but in adults, its main clinical value today is as an oncologic marker, not as a calcium regulator.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Hormones.
- ATA (American Thyroid Association) Guidelines - Medullary Thyroid Carcinoma.
- IFCC - Hormone Assay Standardization.
- Mayo Clinic Laboratories - Calcitonin.
- ARUP Consult - Thyroid Cancer Markers.
- MedlinePlus / NIH - Calcitonin Overview.
- Endocrinology Textbooks - C-Cell Physiology & MEN2.