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A.D.A.M. Medical Encyclopedia [Internet]. Atlanta (GA): A.D.A.M.; 2013.

A.D.A.M. Medical Encyclopedia.

Phosphorus - blood

Phosphorus - serum; HPO4-2, PO4-3; Inorganic phosphate; Phosphorus blood test; Serum phosphorus

Last reviewed: November 17, 2011.

The serum phosphorus test measures the amount of phosphate in the blood.

How the test is performed

A blood sample is needed. For information on how this is done, see: Venipuncture

How to prepare for the test

The health care provider may advise you to stop taking drugs that may affect the test.

How the test will feel

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed

This test is performed to see how much phosphorus in your blood. Kidney, liver, and certain bone diseases can cause abnormal phosphorus levels.

Normal Values

Normal values range from 2.4 - 4.1 milligrams per deciliter (mg/dL).

The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.

What abnormal results mean

Higher than normal levels (hyperphosphatemia) may be due to many different health conditions. Common causes include:

Lower than normal levels (hypophosphatemia) may be due to:

What the risks are

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

  • Excessive bleeding
  • Fainting or feeling lightheaded
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)

Special considerations

The following can affect phosphorous levels:


  2. Yu SLA. Disorders of magnesium and phosphorous. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 121.

Review Date: 11/17/2011.

Reviewed by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

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What works?

  • Interventions for bone disease in children with chronic kidney disease
    Chronic kidney disease (CKD) resulting in reduced kidney function and the need for dialysis and kidney transplant is associated with abnormalities in blood calcium and phosphorus levels leading to high levels of the parathyroid hormone (PTH) and to bone disease. This may result in bone deformities, bone pain, fractures and reduced growth rates. Commonly used treatments (Vitamin D compounds and phosphate binders) aim to prevent or correct these outcomes. However these treatments may raise levels of blood calcium, allow calcium and phosphorus deposition in blood vessels and lead to early cardiovascular disease, which is known to be a problem in adults with CKD. This review identified only 15 small RCTs involving 369 children comparing different vitamin D compounds, different routes and frequencies of administration of vitamin D compounds and different phosphate binders. Only five RCTs reported on growth rates and no differences were detected between treatments. Renal bone disease, as assessed by changes in PTH levels, was improved by all vitamin D preparations regardless of preparation used or the route or frequency of administration. Fewer episodes of high blood calcium levels and lower overall serum calcium levels occurred with the non calcium‐containing binder, sevelamer, compared with calcium‐containing binders. As newer treatments for renal bone disease are developed, comparisons with the current standard therapies will be required in well designed RCTs in children using outcome measures including those of direct clinical relevance to children and their families such as rates of growth, reduction in bone fractures and bone pain and reduction in calcification in blood vessels.
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