What is a parathyroid hormone (PTH) test?

This test measures the level of parathyroid hormone (PTH) in your blood. PTH, is made by your parathyroid glands. They are four pea-sized glands in your neck.

Hormones are chemical messengers in your bloodstream. They control the actions of certain cells or organs. PTH controls the level of calcium in your blood. Calcium is one of the most important minerals in your body. Most of it is stored in your bones and teeth. Having the right amount of calcium in your blood is important for your nerves, muscles, and heart to work properly.

If your calcium blood levels are too low, your parathyroid glands will release just enough PTH into your blood to return your calcium levels to normal. PTH raises your blood calcium by:

• Telling your bones to release calcium into your blood
• Helping your intestines to absorb calcium from the food you eat
• Helping your kidneys to keep calcium in your blood instead of getting rid of it through your urine (pee)

When your calcium blood levels return to normal, your parathyroid glands stop making PTH and your blood PTH levels decrease.

Because the amount of PTH in your blood changes with the amount of calcium in your blood, your health care provider will usually order a calcium blood test along with a PTH test. Comparing the results of both tests helps your provider understand if your parathyroid glands are working properly to control your calcium levels.

Other names: parathormone, intact PTH

What is it used for?

A PTH test may be used to:

• Help find out whether parathyroid disorders are the cause of abnormal blood calcium levels. This is the most common use.
• Help find the cause of abnormally low results on a phosphate blood test. That's because PTH also helps control the amount of phosphate (phosphorus) in blood.
• Monitor people with chronic kidney disease.
• Help find the cause of severe osteoporosis, a condition that causes your bones to become weak and break easily.
• Check whether treatment for a known parathyroid disorder is working.
• Check whether all overactive parathyroid tissue has been removed during surgery to treat parathyroid disorders that cause too much PTH.

Why do I need a PTH test?

You may need a PTH test if you:

• Had a calcium test that showed your blood calcium levels aren't normal.
• Have symptoms of too much calcium in your blood. These symptoms may include:
  • Digestive symptoms, such as:
    • Constipation
    • Nausea and vomiting
    • Abdominal (belly) pain
    • Loss of appetite
  • Increased thirst
  • Urinating (peeing) more than usual
  • Kidney stones
  • Bone, joint, and muscle symptoms, such as weakness, aches, and pains
  • Fatigue
  • A change in mental health, such as depression or confusion
• Have symptoms of too little calcium in your blood. These symptoms can range from mild to severe. They may include:
  • Dry skin, coarse hair, and nails that easily break (after a long period of low levels)
  • Muscle cramps, spasms, or stiffness
  • Tingling in the lips, tongue, fingers, and feet
  • Irregular heartbeat (arrhythmia)
  • Seizures, if calcium levels are extremely low
• Have a parathyroid disorder or chronic kidney disease.

What happens during a PTH test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You probably won't need any special preparations for a PTH test but check with your provider. Some providers may ask you to fast (not eat or drink) before your test. You may also need to take the test at a certain time of day.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

Many health conditions can cause abnormal PTH levels. To understand what your PTH test results mean, your provider will consider the results of other tests, especially a blood calcium test. Your symptoms, medical history, and family history will also be considered.

If your PTH level is higher than normal, it's called hyperparathyroidism. There are two types. The type you have generally depends on your blood calcium level:

• Primary hyperparathyroidism is high PTH levels with high blood calcium levels. This often means that a problem with your parathyroid glands is causing them to make too much PTH. The extra PTH raises your blood calcium levels. Possible causes of primary hyperparathyroidism include:
  • A benign tumor (not cancer) in one of your parathyroid glands, called a parathyroid adenoma. This is the most common cause of high PTH levels.
  • Hyperplasia of your parathyroid glands, which means that they have become larger than normal.
  • A rare inherited condition, such as multiple endocrine neoplasia type 1 or familial hypocalciuric hypercalcemia.
  • Parathyroid cancer, which is rare.

• Secondary hyperparathyroidism is high PTH levels with low blood calcium levels. Your parathyroid glands are working correctly by making extra PTH to try to increase your blood calcium. It's likely that a problem outside of your parathyroid glands is preventing your blood calcium levels from increasing.

  Your provider will probably order more tests to find out what's causing your low blood calcium. Possible causes include:

  • Having low levels of vitamin D (vitamin D deficiency), phosphate, and/or magnesium
  • Not getting enough calcium
  • Digestive disorders, such as malabsorption syndromes, that make it hard for your body to absorb calcium from food
  • Kidney failure, which causes your body to lose too much calcium through urine

If your PTH levels are lower than normal and your blood calcium level is also low, it may mean your parathyroid glands can't make enough PTH. This is called hypoparathyroidism. This condition is less common than hyperparathyroidism. Possible causes include:

• Damage to your parathyroid glands from surgery on your neck or radiation therapy for cancer
• Certain autoimmune disorders that destroy parathyroid tissue
• Certain genetic disorders, such as DiGeorge syndrome, also called 22q11.2 deletion syndrome
• Getting too much vitamin D and/or calcium from supplements or from antacids that contain calcium
• Serious illnesses

If your PTH levels aren't normal when compared to your blood calcium level and other test results, your provider will usually order other blood tests to learn more. If a parathyroid tumor is suspected, you may also have imaging tests. If you have questions about your results, talk with your provider.

Learn more about laboratory tests, reference ranges, and understanding results.