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.

Risks

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.
• Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

Results

A parathyroid hormone (PTH) blood test measures the level of parathyroid hormone in the blood. The test is used to help identify hyperparathyroidism or to find the cause of abnormal calcium levels.

Normal

Normal values may vary from lab to lab. Results are usually available in 1 to 2 days.

High values

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 of the lung, kidney, pancreatic, or ovarian cancer.

Low values

Low PTH levels may be caused by:

• Damage to the parathyroid gland, which can by caused by neck surgery or radiation treatments.
• A rare disease, such as sarcoidosis or histiocytosis X.
• An overdose of vitamin D or calcium.
• Cancer, such as lymphoma or multiple myeloma.
• A low magnesium level.

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 (Betachron ER, Inderal, Inderal LA).
• Being pregnant or breast-feeding.
• Having high cholesterol or triglyceride levels.
• Having a scan that uses a radioactive tracer within 1 week of PTH test.
• Drinking milk or eating milk products right before the test.