A parathyroid hormone (PTH) blood test measures the level of parathyroid hormone in the blood. This test is used to help identify hyperparathyroidism or to find the cause of abnormal calcium levels. PTH controls calcium and phosphorus levels in the blood.
PTH is made by the parathyroid glands, which are four pea-sized glands that lie behind the thyroid gland. If the blood calcium level is too low, the parathyroid glands release more PTH. This causes the bones to release more calcium into the blood and reduces the amount of calcium released by the kidneys into the urine. Also, vitamin D is converted to a more active form, causing the intestines to absorb more calcium and phosphorus. If the calcium level is too high, the parathyroid glands release less PTH, and the whole process is reversed.
PTH levels that are too high or too low can cause problems with the kidneys and bones and cause changes in calcium and vitamin D levels.
Tests for calcium and phosphorus levels in the blood may be done at the same time as a PTH test.
Why It Is Done
A test for parathyroid hormone (PTH) is done to:
How To Prepare
Do not eat or drink anything except water for 8 to 10 hours before the test. A PTH test is usually done shortly after you wake up because PTH levels change once you become active. But your doctor will discuss any changes to this schedule with you. Tell your doctor if you work nights so that you can arrange to have your blood tested shortly after you wake up.
Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results may mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).
How It Is Done
The health professional drawing blood will:
How It Feels
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
There is very little chance of a problem from having blood sample taken from a vein.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Results are usually available in 1 to 2 days.
High PTH levels may be caused by:
Low PTH levels may be caused by:
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
What To Think About
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