What is the phosphorus test?

This test measures the amount of phosphorus in your blood. Phosphorus is a chemical your body needs to get energy from the food you eat. It’s also important for healthy bones.

Phosphorus is also called phosphate. You can get phosphate from food.

Why is this test done?

This test may help diagnose and treat a medical problem you are having. It does not diagnose a specific problem but it can help your healthcare provider know what other tests you might need. It’s also a way to see how well treatment for a disease is working. For example it may be done to:

• Help diagnose kidney failure or to see how well dialysis is working when you have kidney failure.
• To see if you are getting the nutrients your body needs.
• During treatment for diabetic ketoacidosis (a dangerous buildup of acids in the blood from a lack of insulin)
• 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. Ask your provider before stopping any of your regular medicines.
• Talk to your healthcare provider if you have any questions about the test.

How is the test done?

Having this test will take just a few minutes. A small amount of blood is taken from a vein in your arm with a needle. The blood is collected in tubes and sent to a lab.

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

What does the test result mean?

Some of the reasons your phosphorus level may be higher than normal are:

• You have kidney disease.
• Your body is not making enough parathyroid hormone.
• You are having chemotherapy.
• You have a muscle injury.
• You have a severe infection.
• You have been taking phosphorus supplements, or you are getting too much phosphorus in your diet.

Some of the reasons your phosphorus level may be lower than normal are:

• Your body is making too little thyroid hormone or too much parathyroid hormone.
• 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.
• 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, physical exam, and current health. Sometimes a test needs to be repeated to check the first result. Talk to your healthcare provider about the results and ask questions, such as:

• If you need more tests
• What kind of treatment you might need
• What lifestyle, diet, or other changes you might need to make