A parathyroid hormone (PTH) blood test
measures the level of parathyroid
hormone in the blood. This test is used to help
hyperparathyroidism or to find the cause of abnormal
calcium levels. PTH controls calcium and
phosphorus levels in the blood.
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:
- Help identify
- Find the cause of an abnormal blood calcium
- Check to see whether a problem with the
parathyroid glands is causing the abnormal calcium
- Watch for problems in people who have
chronic kidney disease.
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
- Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.
- Clean the needle site with
- Put the needle into the vein. More than one needle stick
may be needed.
- Attach a tube to the needle to fill it with
- Remove the band from your arm when enough blood is
- Put a gauze pad or cotton ball over the needle site as
the needle is removed.
- Put pressure to the site and then put on a