Serum phosphorus

Alternative Names: Phosphorus - serum; HPO4-2, PO4-3; Inorganic phosphate; Phosphorus blood test

The serum phosphorus test measures the amount of phosphate in the blood.

Why is the Test Performed?

This test is performed to check the blood level of phosphorus, particularly if you have a disorder known to cause abnormal phosphorus levels.

How is the Test 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 a 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.

Preparation for the Test

The health care provider may advise you to stop taking drugs that may affect the test.

How will the Test 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.

Serum phosphorus Risks

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)

Considerations

The following can affect phosphorous levels:

  • Antacids
  • Enemas containing sodium phosphate
  • Excess vitamin D supplements
  • Glucose through a vein (intravenous)
  • Laxatives containing sodium phosphate
  • Methicillin

Normal Results for Serum phosphorus

Normal values range from 2.4 - 4.1 milligrams per deciliter (mg/dL).

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.

What Abnormal Results Mean

Higher than normal levels (hyperphosphatemia) may indicate:

Lower than normal levels (hypophosphatemia) may indicate:

Other conditions under which the test may be performed:

Related Images

Review Date: 11/15/2009
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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