Calcitonin

What is calcitonin?

Calcitonin is a hormone your thyroid makes and releases to help regulate calcium levels in your blood by decreasing them. Calcitonin opposes the actions of parathyroid hormone, which increases your blood calcium levels.

Your thyroid is a small, butterfly-shaped gland at the front of your neck under your skin. The C-cells in your thyroid (parafollicular cells) make and secrete calcitonin.

Calcitonin is a unique hormone because scientists don’t fully understand its importance. While they know what it does, they don’t understand why we have it. Irregular calcitonin levels cause few or no symptoms.

Calcitonin as medicine

In the past, healthcare providers prescribed manufactured forms of calcitonin as medicine to treat conditions like Paget’s disease of the bone and hypercalcemia. But with newer medications (like bisphosphonates), providers rarely use calcitonin for treatment.

What is the function of calcitonin?

Calcitonin’s main job is to lower calcium levels in your blood (not your bones). It does this in two main ways:

• Calcitonin blocks the activity of osteoclasts, which are cells that break down bone. When osteoclasts break down your bone, the calcium from your bone goes into your bloodstream. The temporary blocking of osteoclasts by calcitonin reduces the amount of calcium that enters your blood.
• Calcitonin can decrease the amount of calcium your kidneys reabsorb and release back into your bloodstream. This causes lower blood calcium levels.

What stimulates calcitonin release?

Your thyroid releases calcitonin based on the level of calcium in your blood. When your blood calcium levels increase, your thyroid releases calcitonin in higher quantities. When blood calcium levels decrease, your thyroid decreases the amount of calcitonin it releases.

What test measures calcitonin levels?

Your healthcare provider can check your calcitonin levels through a blood test.

Abnormal calcitonin levels don’t cause symptoms. So, providers typically only recommend a calcitonin blood test for the following reasons:

• To help diagnose medullary thyroid cancer (MTC) or C-cell hyperplasia
• To monitor the treatment of MTC
• If you have a family history of multiple endocrine neoplasia (MEN) type 2

What are normal calcitonin levels?

In general, the normal ranges for calcitonin include:

• For people assigned male at birth: Less than 25 pg/mL (picograms per milliliter)
• For people assigned female at birth: Less than 20 pg/mL

Normal ranges for calcitonin levels can vary from lab to lab. Always reference the lab’s normal range on your blood test report.

If you need to get a calcitonin test, your healthcare provider will go over your results. They’ll let you know if you need to get further testing.

What happens when calcitonin levels are too high?

Having a high calcitonin level doesn’t seem to negatively affect your body or cause symptoms. But having high levels of calcitonin may be a sign of two rare conditions, including:

• Medullary thyroid cancer (MTC). This is a rare thyroid cancer that begins in the C-cells of your thyroid — the cells that make calcitonin. MTC can cause those cells to make excess amounts of calcitonin.
• C-cell hyperplasia. This is a benign (noncancerous) condition that causes abnormal C-cell growth. The enlarged tissue can release excess calcitonin. C-cell hyperplasia can sometimes progress to become MTC.

If you have symptoms of either of these conditions, your provider may recommend a calcitonin test.

What happens when calcitonin levels are too low?

Having low levels of calcitonin doesn’t seem to affect your body. People who’ve had their thyroid removed and have undetectable levels of calcitonin have no symptoms related to blood calcium levels.

What’s the difference between parathyroid hormone and calcitonin?

Both parathyroid hormone and calcitonin help regulate the level of calcium in your blood. The difference is how they do so and how much they affect your calcium level.

Parathyroid hormone (PTH) increases your blood calcium level. PTH also helps control the levels of phosphorus in your blood and bones. It activates vitamin D.

Calcitonin decreases your blood calcium level. But PTH seems to have a more important role in regulating your blood calcium levels than calcitonin. Scientists mainly know this because having abnormal levels of PTH can cause hypercalcemia or hypocalcemia. These can be serious conditions. On the other hand, having an abnormal calcitonin level doesn’t have much of an effect on your body.

What’s the difference between calcitonin and calcitriol?

Calcitonin and calcitriol are both hormones that affect calcium levels. But they have different functions. Calcitriol helps increase blood calcium levels. Calcitonin helps decrease these levels.

Calcitriol is a hormone that’s also known as active vitamin D. It increases the amount of calcium your gut can absorb from the food you eat. Your body then releases calcium into your bloodstream. Calcitriol also prevents calcium loss from your kidneys. Parathyroid hormone stimulates the enzyme that transforms vitamin D into calcitriol.