Parathyroid Hormone

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. 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:

• 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.

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.

What To Think About

• Because PTH can raise calcium levels and lower phosphorus levels, blood tests for calcium and phosphorus are often done at the same time as a test for PTH.
• How well your kidneys work can affect how much PTH you have in your blood. For this reason, tests to measure the amount of creatinine in the blood may be done at the same time as a PTH test.
• A high PTH level along with a high calcium level can cause problems such as osteoporosis, kidney stones, high blood pressure, kidney failure, peptic ulcer disease, cognitive changes, and problems with the balance of water in the body. About half of all people who have high levels of PTH and calcium in the blood need treatment to correct the abnormal levels. Further testing, such as bone density testing or 24-hour urine calcium testing, may be needed to help make decisions about treatment.
• An overactive parathyroid gland is often caused by a noncancerous (benign) tumor of the parathyroid gland. Parathyroid tumors tend to grow slowly and may not cause any symptoms for many years. Parathyroid tumors are more common after age 50 and are often found with routine blood tests that are done for other reasons. Treatment includes close observation, medicines, or surgery to remove the tumor.