Parathyroid Hormone (PTH) Test
Reviewed
Also called: Parathormone, Intact PTH
This test measures the level of parathyroid hormone (PTH) in your blood. PTH controls the level of calcium in your blood.
Specimen: blood
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 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.
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.
- Higher than normal PTH with high blood calcium (primary hyperparathyroidism): 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. Limitation: The type you have generally depends on your blood calcium level. Next step: If a parathyroid tumor is suspected, you may also have imaging tests.
- Higher than normal PTH with low blood calcium (secondary hyperparathyroidism): 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. Limitation: It's likely that a problem outside of your parathyroid glands is preventing your blood calcium levels from increasing. Next step: Your provider will probably order more tests to find out what's causing your low blood calcium.
- Lower than normal PTH with low blood calcium (hypoparathyroidism): 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. Limitation: This condition is less common than hyperparathyroidism. Next step: If you have questions about your results, talk with your provider.
- PTH not normal when compared to blood calcium and other results: Many health conditions can cause abnormal PTH levels. Limitation: Your symptoms, medical history, and family history will also be considered. Next step: 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.
- 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
Comparing the results of both tests helps your provider understand if your parathyroid glands are working properly to control your calcium levels. 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
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.
U.S. National Library of Medicine: Parathyroid Hormone (PTH) Test