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Phosphate in Blood

A phosphate test measures the amount of phosphate in a blood sample. Phosphate is a charged particle (ion) that contains the mineral phosphorus. The body needs phosphorus to build and repair bones and teeth, help nerves function, and make muscles contract. Most (about 85%) of the phosphorus contained in phosphate is found in bones. The rest of it is stored in tissues throughout the body.

The kidneys camera.gif help control the amount of phosphate in the blood. Extra phosphate is filtered by the kidneys and passes out of the body in the urine. A high level of phosphate in the blood is usually caused by a kidney problem.

The amount of phosphate in the blood affects the level of calcium in the blood. Calcium and phosphate in the body react in opposite ways: as blood calcium levels rise, phosphate levels fall. A hormone called parathyroid hormone (PTH) regulates the levels of calcium and phosphorus in your blood. When the phosphorus level is measured, a vitamin D level, and sometimes a PTH level, is measured at the same time. Vitamin D is needed for your body to take in phosphate.

The relation between calcium and phosphate may be disrupted by some diseases or infections. For this reason, phosphate and calcium levels are usually measured at the same time.

Why It Is Done

A test to measure phosphate in blood may be done to:

  • Check phosphate levels if you have kidney disease or bone disease.
  • Help find problems with certain glands, such as the parathyroid glands.
  • Find a reason for abnormal vitamin D levels.

How To Prepare

Many medicines can change the results of this test. Be sure to tell your doctor about all the nonprescription and prescription medicines you take, including vitamin D supplements.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).

WebMD Medical Reference from Healthwise

Last Updated: March 18, 2013
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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