Health Encyclopedia


Does this test have other names?

Phosphorus blood test, phosphate test

What is this test?

This test measures the level of phosphorus in your blood. Phosphorus is a common mineral found in the food you eat. It's also found in teeth and bones.

Having a high or low level of phosphorus in your bloodstream can signal a number of health conditions. Most commonly, a high level of phosphorus is related to a kidney disorder. It shows that your kidneys are having difficulty clearing phosphorus from your blood. A high level of phosphorus can also mean uncontrolled diabetes and other endocrine disorders.

Why do I need this test?

You may need a phosphorus test if your healthcare provider suspects that you have a kidney disorder. You may also need this test if you are having trouble controlling your diabetes. You may need this test if you have symptoms of kidney disease, including bone problems, fatigue, and weakness, but you may not have any symptoms at all.

What other tests might I have along with this test?

Phosphorus levels are closely related to calcium levels, so your healthcare provider will probably test your calcium level as well. Additional tests depend on which condition your healthcare provider suspects.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your healthcare provider.

Results of this test are given in milligrams per deciliter (mg/dL). A normal phosphorus reading is between 2.7 and 4.6 mg/dL, but normal ranges may vary. A number that is either higher or lower than that could mean a possible kidney problem.

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Phosphorus levels can be affected by what you eat and drink, including:

  • Chocolate

  • Cheese

  • Fish

  • Many types of beans

  • Beer

  • Cola

Some medicines and medical procedures, such as dialysis, can also affect phosphorus levels.

How do I get ready for this test?

You may need to fast starting at midnight before the test. Ask your healthcare provider for specific instructions.  Be sure your provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use. 

Medical Reviewers:

  • Freeborn, Donna, PhD, CNM, FNP
  • Snyder, Mandy, APRN