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PTH stands for parathyroid hormone. It is a protein hormone released by the parathyroid gland.
The parathyroid glands are located in the neck, near or attached to the back side of the thyroid gland. Parathyroid hormone controls calcium, phosphorus, and vitamin D levels in the blood and bone.
Release of PTH is controlled by the level of calcium in the blood. Low blood calcium levels cause increased PTH to be released, while high blood calcium levels block PTH release.
A laboratory test can be done to measure the amount of PTH in your blood.
Parathormone; Parathormone (PTH) intact molecule; Parathyroid hormone
How the Test is Performed
A blood sample is needed. For information on how this is done, see: Venipuncture
How to Prepare for the Test
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.
How the Test Will Feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the Test is Performed
Your health care provider may order this test if:
- You have high calcium or low phosphorus levels in your blood, and you may have abnormal PTH.
- You have osteoporosis that is severe, cannot be explained, or does not respond to treatment.
Normal values are 10 - 55 picograms per milliliter (pg/mL). To help understand whether your parathyroid hormone levels are normal, your health care provider will measure your blood calcium at the same time.
The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different specimens. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
Parathyroid hormone levels above 55 picograms per milliliter (pg/mL) are considered to be high. These higher levels may be caused by:
- Disorders that increase phosphate or phosphorous levels in the blood, such as chronic kidney disease
- Failure of the body to respond to parathyroid hormone (pseudohypoparathyroidism)
- Lack of calcium, which may be due to not eating enough calcium, not absorbing calcium, 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
Lower-than-normal levels 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 from milk or certain antacids, such as calcium carbonate or sodium bicarbonate (baking soda)
- Low levels of magnesium in the blood
- Radiation to the parathyroid glands
- Vitamin D intoxication
Other conditions under which the test may be performed:
- Excessive bleeding
- Fainting or feeling light-headed
- 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: Kronenberg HM, Melmed S, Polansky KS, Larsen PR, eds. Williams Textbook of Endocrinology. 12th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 28.
Reviewed By: Nancy J. Rennert, MD, Chief of Endocrinology & Diabetes, Norwalk Hospital, Associate Clinical Professor of Medicine, Yale University School of Medicine, New Haven, CT. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.