Parathyroid hormone (PTH) blood test

A blood sample is needed.

Ask your health care provider if you should stop eating or drinking for some period of time before the test. Most often, you will not need to fast or stop drinking.

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.

Parathyroid hormone (PTH) is released by the parathyroid glands. The 4 tiny parathyroid glands are located in the neck, near or attached to the back side of the thyroid gland. The thyroid gland is located in the neck, just above where your collarbones meet in the middle.

PTH controls calcium, phosphorus, and vitamin D levels in the blood. It is important for regulating bone growth. Your provider may order this test if:

• You have a high calcium level or low phosphorus level in your blood.
• You have severe osteoporosis that cannot be explained or does not respond to treatment.
• You have kidney disease

To help understand whether your PTH is normal, your provider will measure your blood calcium at the same time.

Normal values are 10 to 55 pg/mL.

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different specimens. Talk to your provider about the meaning of your specific test results.

A higher-than-normal level may occur with:

• Disorders that increase phosphate or phosphorous levels in the blood, such as chronic kidney disease
• Failure of the body to respond to PTH (pseudohypoparathyroidism)
• Lack of calcium, which may be due to not eating enough calcium, not absorbing calcium in the gut, or losing too much calcium in your urine
• Pregnancy or breastfeeding (uncommon)
• Swelling in the parathyroid glands, called primary hyperparathyroidism
• Tumors in the parathyroid gland, called adenomas
• Vitamin D disorders, including not enough sunlight in older adults and problems absorbing, breaking down, and using vitamin D in the body

A lower-than-normal level may occur with:

• Accidental removal of parathyroid glands during neck surgery
• Autoimmune destruction of the parathyroid gland
• Cancers that start in another part of the body (such as the breast, lungs, or colon) and spread to the bone
• Excess calcium over a long period of time usually from excess calcium supplements or certain antacids, that contain calcium carbonate or sodium bicarbonate (baking soda)
• Parathyroid glands do not produce enough PTH (hypoparathyroidism)
• Low levels of magnesium in the blood
• Radiation to the parathyroid glands
• Sarcoidosis
• Excess vitamin D intake

Other conditions for which the test may be ordered include:

• Multiple endocrine neoplasia (MEN) I
• Multiple endocrine neoplasia (MEN) II

Veins and arteries vary in size from one person to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

• Excessive bleeding
• Fainting or feeling lightheaded
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Bringhurst FR, Demay MB, Kronenberg HM. Hormones and disorders of mineral metabolism. In: Melmed S, Polonsky KS, Larsen PR, Kronenberg HM, eds. Williams Textbook of Endocrinology. 13th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 28.

Chernecky CC, Berger BJ. Parathyroid hormone (PTH) - Blood. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. Philadelphia, PA: Elsevier Saunders; 2013:854-856.