What does calcium have to do with the parathyroid gland?

DEAR DOCTOR K:

A recent blood test showed that the calcium level in my blood is high. My levels of something called “PTH” are also high. Now my doctor has scheduled a parathyroid scan. Why? What does calcium have to do with the parathyroid?

DEAR READER:

You have four parathyroid glands. These pea-sized glands sit on your thyroid gland, in the lower part of your neck. I’ve put an illustration of the parathyroid glands below.

A hormone is a chemical made in one organ that enters the blood, travels throughout the body and affects how different parts of the body work. The parathyroid glands produce the parathyroid hormone (PTH).

The job of the parathyroid glands is to adjust their production of PTH to keep calcium levels in your blood within a normal range. If the calcium level in your blood starts to drop, the parathyroid glands make more PTH. If calcium levels rise, the glands make less hormone.

How does PTH influence calcium levels? In three different ways. Lots of calcium is stored in your bones. PTH causes the bones to release calcium into the blood. PTH also stimulates the intestines to absorb more calcium from food. Finally, PTH signals the kidneys to withhold calcium from the urine.

Parathyroid

Hyperparathyroidism (hi-per-par-a-THIGH-royd-izm) occurs when one (or more) of the parathyroid glands becomes overactive and makes more PTH than it should. Excess hormone is released into the bloodstream. The result is abnormally high levels of calcium and PTH in the blood.

If your hyperparathyroidism is mild, you might not need treatment. But you should have regular blood tests to measure your blood calcium level and make sure it’s not going higher. You will also need periodic bone density tests because PTH causes calcium to leak out of bones, which causes them to thin.

More severe hyperparathyroidism can cause bone pain and thin, brittle bones that are more easily fractured. Elevated levels of PTH and calcium can also trigger the formation of kidney stones and cause kidney damage, dehydration and confusion.

The reason your doctor has ordered an imaging scan is to check for an enlarged parathyroid gland or a parathyroid tumor. Parathyroid cancer is extremely rare. A doctor may never see a single case despite practicing medicine for decades. I never have.

If your condition is severe enough, you may need surgery to remove the affected parathyroid gland(s). If it’s less severe, your doctor may prescribe medication. Drugs used to treat hyperparathyroidism include hormone replacement therapy and bisphosphonates, both of which help bones retain calcium. Another type of drug mimics calcium in the body, in order to trick the parathyroid gland into releasing less PTH.

Fortunately, many people with hyperparathyroidism have a mild condition that never becomes serious enough to require treatment. But it does require regular repeat testing to be sure it’s not getting worse.