What Do Different Blood Test Results Mean in Hypoparathyroidism?

Hypoparathyroidism can have a number of different causes. Therefore, a battery of tests is usually necessary to diagnose it. What each blood test is investigating, and what the results mean, can be confusing for patients and their families.

Here is some information about the most common tests and how their results might relate to hypoparathyroidism.

What is hypoparathyroidism?

The body’s parathyroid glands — four glands attached to the thyroid gland in the neck — produce the parathyroid hormone (PTH), which regulates blood calcium levels. In hypoparathyroidism, these glands do not produce enough functioning PTH.

Low levels of PTH can lead to hypocalcemia, or inadequate levels of calcium, needed for bone growth and bone cell activity. Hypocalcemia can cause symptoms such as muscle spasms, tingling sensations, cramps, and even seizures.

Types of blood tests for the diagnosis of hypoparathyroidism

There is no single test to diagnose hypoparathyroidism. Your doctor will use a variety of blood tests, along with reviewing your symptoms and medical history, to aid in diagnosis.

The most common blood tests are these:

Blood calcium levels

A blood-calcium level test, which also may be called a total calcium or ionized calcium test, will check the levels of calcium in your blood. Calcium is a mineral that is very important in the body for functions such as communication between cells, contractions of the heart and skeletal muscles, blood clotting, and maintenance of bone health. Abnormal levels of calcium could be an indicator of hypoparathyroidism as PTH and calcium levels are linked.

PTH test

Your physician would order a PTH test if he or she suspects you may have hypoparathyroidism. This test is often ordered together with a calcium blood test to see the relationship between the two in the blood.

The parathyroid glands release PTH in response to low blood calcium levels. This, in turn, causes the release of calcium from bones, increases the absorption of calcium from food in the intestines, and decreases the amount of calcium that the kidneys excrete. Ultimately, these responses raise blood calcium levels.

The relationship between the blood levels of PTH and calcium can help with disease diagnosis:

• If both PTH and calcium levels are normal, then both systems seem to be operating correctly.
• If calcium levels are low but PTH levels are high, the PTH system appears to be functioning correctly. Thus, other testing will be necessary to determine why the calcium levels are low.
• If calcium levels are low and PTH levels are low or normal, then you may have hypoparathyroidism
• If both calcium and PTH levels are high, you may have hyperparathyroidism. This is a different disorder in which the body produces too much PTH.
• If calcium levels are high and PTH levels are low, the PTH system appears to be working. Your physician may recommend further testing to determine why the calcium levels are high.

Vitamin D levels

Vitamin D is important for the body to absorb calcium. Low levels of vitamin D can contribute to low levels of calcium. Your body can get vitamin D either from foods or supplements, or by creating its own during exposure to sunlight. If your vitamin D levels are low, your physician may recommend supplements. 

Phosphorus test

While PTH has the largest effect on blood calcium levels, it also has an inverse, or opposite effect on phosphorus levels in the blood. For this reason, your doctor may recommend you have a blood phosphorus (phosphate) test for an initial diagnosis and again later, to monitor phosphorus levels in your blood.

Phosphorus is an element that exists as phosphate in nature. Phosphate levels are what is actually measured in a blood phosphorus test. Patients with hypoparathyroidism often exhibit hyperphosphatemia or too much phosphate and may have to reduce their dietary intake of phosphorus.

Magnesium test

Magnesium is another mineral element that is critical to bodily functions, including the production of energy, cell signaling, and the control of blood pressure and glucose levels. Research has shown that magnesium also plays a role in the production of PTH, with high magnesium levels leading to a reduction in PTH production. Physicians can use the blood magnesium test to investigate whether magnesium levels are high in your body and if it could be affecting PTH production.

Last updated: Sept. 11, 2020

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