Calcitonin: Low vs High Signs, Testing, Bone Health, and Thyroid Risk
Overview
Calcitonin is a hormone made by C cells in the thyroid gland that helps regulate calcium balance and bone turnover. In everyday physiology its effects are modest compared with other regulators like parathyroid hormone and vitamin D, but calcitonin becomes clinically important as a tumor marker in specific thyroid conditions. Clinicians mostly think about calcitonin when evaluating thyroid nodules, suspected medullary thyroid carcinoma, or when following people who already have this diagnosis.
In practice, calcitonin is almost always interpreted together with Parathyroid Hormone and calcium related markers so that both thyroid derived and parathyroid derived calcium signals can be viewed in context.
What Calcitonin is and where it is made
Calcitonin is a peptide hormone produced by parafollicular C cells in the thyroid gland.
It is released into the bloodstream in response to rising blood calcium levels.
While present throughout life, its day to day role in human calcium regulation is smaller than that of parathyroid hormone and vitamin D.
What Calcitonin does in your body
Helps lower blood calcium levels by reducing bone resorption, the process where bone is broken down and calcium is released into the blood.
May modestly promote calcium deposition in bone under some conditions.
Plays a larger regulatory role in some animals than in humans, but in humans is most useful as a marker of C cell activity rather than a primary calcium control knob.
When testing Calcitonin makes sense
Evaluation of thyroid nodules when there is concern about medullary thyroid carcinoma.
Screening in people with a strong family history or known genetic risk of medullary thyroid carcinoma or related syndromes, when recommended by a specialist.
Monitoring after treatment for medullary thyroid carcinoma to assess for residual or recurrent disease.
Selected complex calcium or bone evaluations in specialist endocrine settings, usually alongside other markers.
Calcitonin is not a routine screening test for the general population and is typically ordered by endocrinologists or thyroid specialists.
How to think about high and low Calcitonin results
This information is general and does not replace lab specific reference ranges or medical evaluation.
Low or undetectable calcitonin might be associated with:
Normal thyroid C cell activity in people without medullary thyroid carcinoma.
Removal of the thyroid gland, especially when C cells have been taken out with surgery.
Low values are usually reassuring in the contexts where calcitonin is used and are seldom a problem by themselves.
High calcitonin might be associated with:
Medullary thyroid carcinoma, especially when levels are clearly and persistently elevated.
C cell hyperplasia, a condition where C cells are increased but not always cancerous, sometimes seen in high risk families.
Some other neuroendocrine tumors, severe kidney disease, or certain medications, although these are less common explanations.
Because modest elevations can have several causes and calcitonin can be influenced by assay method and stimulation tests, interpretation and next steps are best handled by a specialist who can correlate the value with imaging and clinical findings.
What can influence your Calcitonin levels
Thyroid C cell health, including hyperplasia or medullary thyroid carcinoma.
Kidney function, with advanced kidney disease sometimes raising calcitonin levels.
Use of certain medications, including some proton pump inhibitors and other agents in selected reports.
Acute physiological stress, inflammation, or major illness in some cases.
Laboratory method and whether stimulation testing was used as part of the protocol.
When to talk to a clinician about Calcitonin
Calcitonin levels above the reference range, especially when you have thyroid nodules or a family history of medullary thyroid carcinoma.
Ongoing follow up after surgery or treatment for medullary thyroid carcinoma, when trends in calcitonin over time matter.
New neck symptoms, thyroid enlargement, or lymph node changes with a known history of elevated calcitonin.
Questions about whether your family history warrants genetic testing or calcitonin screening.
An endocrinologist or thyroid specialist can review calcitonin results alongside ultrasound, other thyroid labs, genetic risk, and imaging to decide whether observation, more testing, or intervention is appropriate.
Calcitonin in one view
Calcitonin is a thyroid C cell hormone with a modest everyday role in calcium balance but a major role as a marker for certain thyroid C cell conditions, especially medullary thyroid carcinoma. On its own the number is less important than how it changes over time and how it fits with thyroid imaging and other calcium markers such as Parathyroid Hormone, so any elevation is best reviewed with a specialist rather than interpreted in isolation.
