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(P; Phosphate)

What Is Phosphorus?

Phosphorus is a mineral. It is related to how the body uses calcium. Phosphorus is needed for healthy bones and teeth. It also helps the body use energy.

Reason for the Test

The test checks the level of phosphorus in the blood. A phosphorus test may be needed to:

  • Find the cause of problems with how the body uses phosphorus, calcium, or magnesium
  • Find the cause of symptoms related to problems with calcium levels in the blood
  • Watch levels in people with diabetes, a pH imbalance, or problems with parathyroid hormone or vitamin D
  • Check how severe kidney disease is

Type of Sample Taken

A blood sample will be taken from a vein in the arm.

Prior to Collecting the Sample

Tell your doctor about any medicines or supplements you are taking. They may affect the test results. You may be asked to fast for 6 to 8 hours before the test.

During the Sample Collection

You will be asked to sit. An area inside your elbow will be cleaned. A large band will be tied around your arm. The needle will then be inserted into a vein. A tube will collect the blood from the needle. The band on your arm will be removed. Once all the blood is collected, the needle will be removed. Some gauze will be placed over the site to help stop bleeding. You may also be given a bandage to place over the site. The process takes about 5 to 10 minutes.

After Collecting the Sample

After the blood sample is taken, you may need to stay seated for 10 to 15 minutes. If you are lightheaded, you may need to stay seated longer. When you feel better, you can leave.

A bit of blood may ooze from the vein beneath the skin. It will cause a bruise. Firm pressure over the site after the needle is removed will decrease the chance of a bruise. A bruise will usually fade in a day or 2.

Call your doctor right away if you have redness, swelling, lasting bleeding, or pain.


Results may take many days.

Normal phosphorus levels change with your age. A normal result does not mean you do not have a health problem. Osteoporosis can happen with normal phosphorus levels. A phosphorus test is one of a group of tests done to find a cause of problems with phosphorus, calcium, or other levels.

Higher than normal phosphorus levels can mean:

  • Low calcium levels
  • Kidney failure
  • Hypoparathyroidism
  • High levels of vitamin D
  • Diabetic ketoacidosis or lactic acidosis
  • Cancer that has spread to the bones
  • Too much growth hormone from the pituitary gland

Lower than normal phosphorus levels can mean:

  • Hyperparathyroidism
  • High calcium levels
  • Low potassium levels
  • Alcohol use disorder
  • Malnutrition
  • Thyroid problems
  • Bone problems caused by low vitamin D levels
  • Kidney problems

Your doctor will talk to you about the results. A test may point to an illness that you do not have. It can also miss an illness that you may have. The doctor will check your symptoms and all test results before making a diagnosis.


Phosphorus. Lab Tests Online—American Association for Clinical Chemistry website. Available at: https://labtestsonline.org/tests/phosphorus. Updated December 21, 2018. Accessed July 25, 2019.

Phosphate measurement. EBSCO DynaMed website. Available at:http://www.dynamed.com/topics/dmp~AN~T907115/Phosphate-measurement. Updated October 8, 2019. Accessed July 25, 2019.

Last reviewed June 2019 by EBSCO Medical Review Board Nicole S. Meregian, PA  Last Updated: 10/23/2019