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PTH

Definition:

PTH is a test that measures the amount of PTH (parathormone) in blood.

Alternative Names:

Parathormone; Parathormone (PTH) intact molecule; Parathyroid hormone

How the test is performed:

Adult or child:

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to fill with blood. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. The tourniquet is then removed to restore circulation. After blood has been collected the needle is removed, and the puncture site is covered to stop any bleeding.

Infant or young child:

The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding.

How to prepare for the test:

Fasting (except water) is required 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:

This test may be performed when PTH abnormality is suspected as a cause of abnormal calcium or phosphorus levels.

PTH, the most important regulator of body calcium and phosphorus, is a protein hormone secreted by the parathyroid gland.

PTH:

Increases calcium and phosphorus release from bone
Decreases the loss of calcium and increases the loss of phosphorus in the urine
Increases the activation of 25-hydroxy vitamin D to 1,25-dihydroxy vitamin D in the kidneys

Secretion of PTH is regulated by the level of calcium in the blood. Low serum calcium causes increased PTH to be secreted, whereas increased serum calcium inhibits PTH release.

Review Date: 3/3/2006
Reviewed By: David Juan, MD, Specializing in Endocrinology Issues, Good Hand Medical Center and Alperin Medical Clinics, Santa Clara, CA. Review provided by VeriMed Healthcare Network.

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