Parathyroid Hormone (PTH) Test

Why this test may be ordered

• To help find out whether parathyroid disorders are the cause of abnormal blood calcium levels.
• To help find the cause of abnormally low results on a phosphate blood test.
• To monitor people with chronic kidney disease.
• To help find the cause of severe osteoporosis.
• To check whether treatment for a known parathyroid disorder is working.

Preparation and collection

You probably won't need any special preparations, 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.

A health care professional will take a blood sample from a vein in your arm, using a small needle. This usually takes less than five minutes.

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.

Understanding results

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.

• Higher than normal PTH with high blood calcium (Primary hyperparathyroidism): This often means that a problem with your parathyroid glands is causing them to make too much PTH. Possible causes include a benign tumor (parathyroid adenoma), hyperplasia of the parathyroid glands, a rare inherited condition, or parathyroid cancer (rare). Limitation: Further tests and imaging may be needed to determine the exact cause. Next step: Prompt
• Higher than normal PTH with low blood calcium (Secondary hyperparathyroidism): Your parathyroid glands are working correctly by making extra PTH to try to increase your blood calcium. It is likely that a problem outside of your parathyroid glands is preventing your blood calcium levels from increasing. Possible causes include low levels of vitamin D, phosphate, and/or magnesium; not getting enough calcium; digestive disorders; or kidney failure. Limitation: Your provider will probably order more tests to find out what is causing your low blood calcium. Next step: Prompt
• Lower than normal PTH with low blood calcium (Hypoparathyroidism): It may mean your parathyroid glands cannot make enough PTH. Possible causes include damage to your parathyroid glands from surgery or radiation, certain autoimmune disorders, certain genetic disorders, getting too much vitamin D and/or calcium from supplements or antacids, or serious illnesses. Limitation: This condition is less common than hyperparathyroidism. Next step: Prompt
• PTH levels not normal when compared to 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. Limitation: Additional testing is needed to clarify the diagnosis. Next step: Prompt

• The test alone does not diagnose a condition; results must be interpreted alongside calcium levels, symptoms, medical history, and family history.
• There is very little risk to having a blood test; you may have slight pain or bruising at the needle site, but most symptoms go away quickly.

What to do next

If you have questions about your results, talk with your provider.

• What do my PTH and calcium levels together indicate about my parathyroid function?
• Do I need any additional tests or imaging based on my results?
• How often should I have this test repeated?

Evidence source

U.S. National Library of Medicine: Parathyroid Hormone (PTH) Test