Calcitonin is a hormone that plays a role in maintaining the body’s balance. It is involved in regulating calcium levels in the bloodstream. Its presence and levels offer insights into certain bodily processes, particularly those related to calcium management.
Understanding Calcitonin
Calcitonin is a hormone produced by specialized cells within the thyroid gland, known as C-cells or parafollicular cells. These cells are distinct from the follicular cells that produce thyroid hormones like T3 and T4. The primary purpose of calcitonin is to regulate the levels of calcium and phosphate in the blood.
Calcitonin acts to reduce calcium levels in the blood, working in opposition to parathyroid hormone (PTH), which increases blood calcium. Its secretion is influenced by the concentration of calcium in the blood; higher calcium levels stimulate increased calcitonin release.
Calcitonin’s Role in Calcium Balance
Calcitonin influences calcium and phosphate levels through specific mechanisms, primarily by acting on bone and kidneys. Its main action involves inhibiting the activity of osteoclasts, which are cells responsible for breaking down bone tissue. When osteoclasts break down bone, calcium stored within the bone is released into the bloodstream. Calcitonin reduces the amount of calcium entering the blood by blocking osteoclast activity.
Calcitonin also affects the kidneys, decreasing the reabsorption of calcium and phosphate back into the bloodstream. This leads to increased excretion of these minerals in the urine.
Testing Calcitonin Levels
A calcitonin test measures the amount of this hormone in a blood sample. Doctors may order this test for several reasons, most commonly to aid in diagnosing C-cell hyperplasia or medullary thyroid carcinoma (MTC). MTC is a rare form of thyroid cancer that originates in the C-cells and can lead to elevated calcitonin production.
The test is also used to monitor the effectiveness of MTC treatment, such as after surgery to remove the thyroid gland, and to check for cancer recurrence. It can also be used for screening individuals with a family history of Medullary Thyroid Carcinoma or Multiple Endocrine Neoplasia type 2 (MEN 2), a genetic disorder that increases MTC risk. Normal calcitonin levels can vary between laboratories, with typical values often less than 25 picograms per milliliter (pg/mL) for males and less than 20 pg/mL for females.
Interpreting Elevated Calcitonin Levels
Elevated calcitonin levels indicate that the C-cells in the thyroid gland are producing excessive amounts of the hormone. The most common cause of high calcitonin is Medullary Thyroid Carcinoma (MTC), a rare but serious cancer. Significantly elevated levels, such as those greater than 20 times the upper limit of normal, are a strong indicator of MTC or C-cell hyperplasia.
Other conditions can also lead to increased calcitonin, including C-cell hyperplasia, a non-cancerous overgrowth of C-cells that may sometimes progress to MTC. Chronic kidney disease can also cause elevated calcitonin, as can certain other cancers like those of the lung, breast, or pancreas, and some gastrointestinal tumors. High calcitonin levels alone do not provide a definitive diagnosis; further medical investigation, including additional tests like a thyroid biopsy, scan, or ultrasound, is necessary to determine the underlying cause.