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Serum Phosphorus

Serum Phosphorus

Alternate Names

  • Phosphorus
  • PO4


Serum phosphorus measures the amount of phosphorus (called phosphate) in the blood or serum. Phosphorus is a mineral that is found in all cells in the body and is critical to bone metabolism. It is also present in proteins and enzymes essential to energy transfer and life (called "ATP").

Who is a candidate for the test?

If a healthcare professional suspects one of the conditions that result from too high or too low a level of phosphorus, he or she may order this test which measure phosphate with calcium levels.

How is the test performed?

In order to measure the amount of phosphorus in the blood, a blood sample is taken from a vein on the forearm or hand. First, the skin over the vein is cleaned with an antiseptic. Next, a rubber tube called a tourniquet is tied around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them. A fine needle is gently inserted into a vein, and the tourniquet is removed. Blood flows from the vein through the needle and is collected in a syringe or vial for testing in the laboratory. After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.

What is involved in preparation for the test?

Normally, no preparation is required for this test.

What do the test results mean?

The normal range for phosphorus in the blood depends on the age and gender of the person. The normal range is between 2.3 and 4.5 mg/dL (milligrams per deciliter).
Decreased phosphorus in the blood could be a result of:
  • alcohol withdrawal
  • parathyroid disease (too much hormone)
  • heavy breathing that decreases carbon dioxide in the blood (called respiratory alkalosis)
  • nutrition problems, especially high sugar feeding after a prolonged, severe fast (candy in concentration camp survivors)
High levels of phosphorus in the blood could be a result of:
  • kidney failure
  • severe injury to the muscle
  • antacids containing aluminum
  • a blood cancer called multiple myeloma

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