Serum calcitonin is a hormone produced primarily by the C cells (parafollicular cells) of the thyroid gland. Its main role is to regulate calcium levels in the blood by lowering blood calcium levels when they are too high. Although calcitonin plays a relatively minor role in calcium regulation compared to parathyroid hormone, it is a useful biomarker in diagnosing certain medical conditions, particularly thyroid diseases and cancer.
What is Serum Calcitonin?
Calcitonin is a peptide hormone that helps regulate calcium homeostasis by lowering blood calcium levels. When blood calcium levels are too high, calcitonin inhibits the release of calcium from bones into the bloodstream, thereby reducing calcium levels. It also reduces calcium reabsorption in the kidneys and limits calcium absorption in the intestines.
Though calcitonin’s physiological role is important, it is not as influential as other hormones such as parathyroid hormone or vitamin D in regulating calcium balance in the body.
Clinical Importance of Serum Calcitonin
While calcitonin’s primary function is to regulate calcium levels, measuring serum calcitonin can be an important diagnostic tool in several medical conditions, particularly in thyroid diseases.
1. Medullary Thyroid Cancer (MTC)
- Medullary thyroid cancer is a type of thyroid cancer that arises from the C cells of the thyroid, which produce calcitonin. In these cases, the levels of serum calcitonin are often abnormally high.
- Elevated calcitonin levels are one of the most specific biomarkers for MTC, and measuring these levels can help confirm the diagnosis of this cancer, particularly when other imaging or biopsy results are inconclusive.
2. Thyroid Disorders
- Hypercalcemia: In cases of hypercalcemia (high blood calcium levels), calcitonin can be used to assess the body’s response to the condition. Calcitonin’s role is to lower calcium levels, and elevated calcitonin levels may indicate that the body is trying to compensate for high calcium levels.
- Thyroid Nodules: Elevated serum calcitonin levels can also be a sign of thyroid nodules or other thyroid-related conditions, which might require further investigation.
3. C-cell Hyperplasia
- C-cell hyperplasia is a condition where there is an overgrowth of the calcitonin-producing cells in the thyroid. This condition can be a precursor to medullary thyroid cancer, and elevated serum calcitonin can serve as an early warning marker.
4. Screening for Hereditary Conditions
- Some inherited syndromes, such as Multiple Endocrine Neoplasia type 2 (MEN2), which includes medullary thyroid cancer, can lead to elevated serum calcitonin levels. Genetic testing and serum calcitonin measurement can be used to screen individuals at risk of developing MTC.
5. Diagnostic Use in Other Cancers
- Though calcitonin is primarily associated with thyroid cancer, it has also been explored as a potential biomarker for other cancers, such as lung cancer or small-cell lung carcinoma, though its use in these contexts is not as widely accepted.
Normal Range of Serum Calcitonin
The normal range for calcitonin levels in the blood can vary depending on the laboratory and the specific assay used, but generally, normal levels are considered to be:
- For men: Less than 5.0 pg/mL
- For women: Less than 5.0 pg/mL
Levels above the normal range, especially if consistently elevated, may suggest a pathological condition, such as medullary thyroid cancer or C-cell hyperplasia.
How is Serum Calcitonin Measured?
Serum calcitonin levels are measured through a blood test. The test is typically ordered when a doctor suspects thyroid-related conditions, particularly medullary thyroid cancer, or when there are symptoms of abnormal calcium metabolism, such as unexplained high calcium levels.
The Process of Testing:
- Blood Sample: A healthcare professional will draw a blood sample, usually from a vein in the arm.
- Lab Analysis: The sample is sent to a laboratory, where it is analyzed for the concentration of calcitonin.
- Results Interpretation: Elevated serum calcitonin levels may suggest medullary thyroid cancer, hypercalcemia, or other thyroid-related issues.
What Elevated Serum Calcitonin Levels May Indicate
Elevated levels of serum calcitonin can indicate several conditions, the most concerning of which is medullary thyroid cancer (MTC). Some of the common causes of increased calcitonin levels include:
1. Medullary Thyroid Cancer (MTC)
- Medullary thyroid cancer is the most well-known cause of elevated calcitonin levels. The C cells of the thyroid, which produce calcitonin, can become cancerous, leading to MTC. The higher the calcitonin level, the more likely it is that the person has MTC.
2. C-cell Hyperplasia
- C-cell hyperplasia refers to the abnormal growth of the C cells in the thyroid, which can sometimes lead to medullary thyroid cancer. Elevated calcitonin levels can be an early sign of this condition.
3. Other Thyroid Disorders
- Elevated calcitonin levels can also occur in people with thyroid nodules or chronic thyroiditis. These conditions may cause calcitonin to be elevated, but to a lesser extent than in MTC.
4. Hypercalcemia
- Hypercalcemia (elevated blood calcium levels) can stimulate the release of calcitonin, as it helps lower calcium levels. This is often seen in conditions like hyperparathyroidism or certain types of cancer, such as lung cancer or multiple myeloma.
5. Hereditary Conditions
- Multiple Endocrine Neoplasia type 2 (MEN2) is a genetic condition that increases the risk of medullary thyroid cancer and other endocrine tumors. Individuals with MEN2 may have elevated calcitonin levels as part of their disease process.
6. Other Cancers
- Some studies suggest that elevated calcitonin may be seen in cancers like small-cell lung carcinoma or pancreatic cancer, though this is less common and not used as a standard diagnostic marker for these cancers.
What Low or Normal Serum Calcitonin Levels Indicate
A normal or low serum calcitonin level is usually a reassuring sign that the thyroid and calcium regulation are functioning normally. However, it does not rule out thyroid diseases, especially in the early stages of medullary thyroid cancer or C-cell hyperplasia, where calcitonin levels may still be within the normal range.
Treatment for Conditions Associated with Elevated Serum Calcitonin
1. Medullary Thyroid Cancer (MTC)
- If MTC is diagnosed based on elevated calcitonin levels, the main treatment is surgical removal of the thyroid gland (thyroidectomy). In some cases, additional treatments like radiation therapy or targeted therapies may be used.
2. C-cell Hyperplasia
- C-cell hyperplasia may require close monitoring, as it can progress to MTC. Early intervention may involve surgery or regular monitoring of calcitonin levels.
3. Hypercalcemia
- If elevated calcitonin levels are linked to hypercalcemia, the underlying cause (such as parathyroid disease or cancer) must be treated. Management may involve medication, surgery, or other therapies depending on the cause.
Conclusion
Serum calcitonin is a valuable marker in the diagnosis and management of medullary thyroid cancer, C-cell hyperplasia, and other thyroid and calcium-related disorders. While its role in calcium homeostasis is limited compared to other hormones, elevated calcitonin levels can provide critical insights into the presence of MTC, a potentially life-threatening cancer. Regular monitoring and early detection of abnormal calcitonin levels are important for effective treatment and improving outcomes for individuals at risk for thyroid cancers and related conditions. If you have concerns about calcitonin levels or thyroid health, discussing testing options with your healthcare provider is essential for early intervention.