PTH

Definition

PTH stands for parathyroid hormone. It is a protein hormone released by the parathyroid gland. PTH is the most important regulator of the body's calcium and phosphorus levels.

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 inhibit PTH release.

A laboratory test can be done to measure the amount of PTH in your blood.

Alternative Names

Parathormone; Parathormone (PTH) intact molecule; Parathyroid hormone

How the test is performed

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

How to prepare for the test

You should not eat or drink anything except water for 10 to 12 hours before the test.

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 doctor may order this test if you have abnormal calcium or phosphorus levels, and a PTH abnormality is suspected.

Normal Values

Normal values are 10 - 55 picograms per milliliter (pg/mL). Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What abnormal results mean

Greater than normal levels may occur with:

• Chronic kidney failure
• Familial hypocalciuric hypercalcemia (FHH)
• High phosphate levels (hyperphosphatemia)
• Hyperparathyroidism
• Increased blood lipids
• Malabsorption syndrome
• Osteomalacia in adults
• Pregnancy or breastfeeding
• Pseudohypoparathyroidism
• Rickets in children
• Use of certain medications such as rifampin, anticonvulsants, diuretics, lithium, and those containing phosphate
• Vitamin D deficiency

Lower than normal levels may occur with:

• Accidental removal of parathyroid glands during neck surgery
• Autoimmune destruction of parathyroid gland
• Hypomagnesemia
• Hypoparathyroidism
• Metastatic bone tumor
• Milk-alkali syndrome (taking too much calcium)
• Radiation to the parathyroid glands
• Sarcoidosis
• Vitamin D intoxication

Other conditions under which the test may be performed:

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

What the risks are

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

Special considerations

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References

Wysolmerski JJ, Insogna KL. The parathyroid glands, hypercalcemia, and hypocalcemia. In: Kronenberg HM, Schlomo M, Polansky KS, Larsen PR, eds. Williams Textbook of Endocrinology. 11th ed. St. Louis, MO: WB Saunders; 2008:chap 266.