A parathyroid hormone (PTH) blood test measures the level of parathyroid hormone in the blood. This test is used to help identify hyperparathyroidism , to find the cause of abnormal calcium levels, or to check the status of chronic kidney disease. 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:
- Help identify hyperparathyroidism.
- Find the cause of an abnormal blood calcium level.
- Check to see whether a problem with the parathyroid glands is causing the abnormal calcium level.
- Watch for problems in people who have chronic kidney disease.
How To Prepare
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.
How It Is Done
The health professional drawing blood will:
- 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 alcohol.
- Put the needle into the vein. More than one needle stick may be needed.
- Attach a tube to the needle to fill it with blood.
- Remove the band from your arm when enough blood is collected.
- 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 bandage.
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.
- You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
- In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
Results are usually available in 1 to 2 days.
Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.
High PTH levels may be caused by:
- A parathyroid gland growth (hyperplasia) or a parathyroid tumor.
- A low level of calcium in the blood. A low blood calcium level can be caused by kidney disease, kidney failure, severe vitamin D deficiency, or an inability of the intestines to absorb calcium from food.
- Some types of cancer, such as lung, kidney, pancreatic, or ovarian cancer.
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:
- Taking medicine that raises PTH levels. These include lithium, furosemide, rifampin, anticonvulsants, thiazide diuretics , and medicines that contain phosphate.
- Taking medicine that lowers PTH levels. These include cimetidine (Tagamet) and propranolol (Inderal, Innopran).
- Being pregnant or breastfeeding.
- Having high cholesterol or triglyceride levels.
- Having a scan that uses a radioactive tracer within 1 week of PTH test.
Current as of: March 31, 2020
Author: Healthwise Staff
E. Gregory Thompson MD - Internal Medicine
Kathleen Romito MD - Family Medicine
Matthew I. Kim MD - Endocrinology