Phosphorus Test

What is the phosphorus test?

The phosphorus test measures the amount of phosphorus (or phosphate) in your blood. 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 phosphorus level may be measured:

• to monitor some medical treatments, such as dialysis.
• to help diagnose some diseases, such as kidney failure
• during treatment for diabetic ketoacidosis
• to see if you are getting the nutrients your body needs
• to help your healthcare provider understand the cause of a low calcium level.

How do I prepare for this test?

• You may need to avoid taking certain medicines before the test because they might affect the test result. Make sure your healthcare provider knows about any medicines, herbs, or supplements that you are taking. Don't stop any of your regular medicines without first consulting with your healthcare provider.
• Talk to your provider if you have any questions about the test.

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.

How will I get the test result?

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

What does the test result mean?

The normal blood phosphorus 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 phosphorus 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.
• You have been taking phosphorus supplements or getting too much in your diet.
• Your parathyroid hormone level is low.

Your blood level of phosphorus may lower than normal if:

• You have been taking antacids for a long time.
• Your calcium level is high.
• You are unable to eat or absorb food.
• You drink too much alcohol.
• You have kidney disease.
• Your body is making too little thyroid hormone or too much parathyroid hormone.
• You have been severely burned.

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 healthcare provider:

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