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What is a Parathyroid Hormone (PTH) Test?
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.
- 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.
Normal values are 10-55 pg/mL. Normal value ranges may vary slightly among different laboratories.
Note: pg/mL = picograms per milliliter
What abnormal results mean:
Greater-than-normal levels may be associated with:
- Chronic renal failure
- Malabsorption syndrome (inadequate absorption of nutrients in the intestinal tract)
- Osteomalacia (adults)
- Rickets (children)
- Vitamin D deficiency
- Pregnancy or breast feeding
- Increased blood lipids
- Medications such as rifampin, anticonsulsants, diuretics, lithium, and those containing phosphate
Lower-than-normal levels may be associated with:
- Autoimmune destruction of parathyroid gland
- Metastatic bone tumor
- Milk-alkali syndrome (excessive calcium ingestion)
- Vitamin D intoxication
- Parathyroid glands that were accidentally removed in neck surgery
Additional 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 lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
- Multiple punctures to locate veins
Veins and arteries vary in size from one patient 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.