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PTH-related Protein

Definition

PTH-related protein is a blood test that measures the amount of a protein molecule similar to parathyroid hormone.

Alternative Names

PTHrp

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

No special preparation is necessary.

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 is done to determine whether high blood calcium levels are caused by an increase in PTH-related protein.

PTH-related protein is produced by some cancers, including those of the lung, breast, head, neck, bladder, and ovaries, as well as leukemia and lymphoma. High levels of PTH-related protein are the cause of high calcium levels in about two-thirds of cancer patients. This condition is called humoral hypercalcemia of malignancy (HHM).

Normal Values

No detectable (or minimal) PTH-like protein is normal.

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

Increased levels of PTH-related protein in a patient with high blood calcium levels generally means that cancer is the underlying cause.

What the risks are

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.

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)

References

Liao J, McCauley LK. Skeletal metastasis: established and emerging roles of parathyroid hormone related protein (PTHrP). Cancer Metastasis Res. 2006;25(4):559-571.

Strewler GJ. The parathyroid hormone-related protein. Endocrinol Metab Clin North Am. 2000;29:629-645.

Review Date: 10/14/2009

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