Blood (Serum) Phosphate or Phosphorus Level Test

What is the blood phosphate test?

This test measures the amount of phosphate in your blood. Phosphate, also called phosphorus, is a chemical your body needs to get energy from the food you eat. Like calcium, it is an important component of bones and you need vitamin D to absorb it. Your body gets phosphate from foods.

Why is this test done?

Your blood phosphate level may be measured to monitor some medical treatments, such as dialysis. This test may also be done to help diagnose illnesses such as kidney failure.

How do I prepare for this test?

• You don't need to fast or limit your activity before the test.
• You may need to avoid taking certain medicines before the test because they might affect the test result. Make sure your health care provider knows about any medicines, herbs, or supplements that you are taking.
• Talk to your health care provider if you have any questions.

How is the test done?

A small amount of blood is taken from your arm with a needle. The blood is collected in tubes and sent to a lab.

Having this test will take just a few minutes of your time. There is no risk of getting AIDS, hepatitis, or any other blood-borne disease from this test.

How will I get the test result?

Ask your health care provider when and how you will get the result of your test.

What does the test result mean?

The normal blood phosphate range for adults in most labs is 2.5 to 4.5 milligrams per deciliter (mg/dL). The normal range may vary slightly from lab to lab. It is usually shown next to your results in the lab report.

Your blood level of phosphate may be higher than normal if:

• You have kidney disease.
• Your body needs more calcium.
• Your body needs more magnesium.
• You are having chemotherapy.
• Your body has too much vitamin D.
• You have muscle damage, for example, from too much exercise.
• You have a severe infection.

Your blood level of phosphate may lower than normal if:

• You have been taking antacids for a long time.
• You are unable to eat or absorb food.
• You drink too much alcohol.
• You have kidney disease.
• Your body is making too much thyroid or parathyroid hormone.
• You have been severely burned.
• You are taking medicine that makes it hard for your body to absorb phosphate.

What if my test result is not normal?

Test results are only one part of a larger picture that takes into account your medical history and current health. Sometimes a test needs to be repeated to check the first result. Talk to your provider about the results and ask questions.

If your test results are not normal, ask your health care provider:

• if you need additional tests
• what you can do to work toward a normal value
• when you need to be tested again.