Also Known As
P
PO4
Phosphate
Formal Name
Inorganic Phosphate
This article was last reviewed on
This article waslast modified on
May 25, 2018.
At a Glance
Why Get Tested?

To evaluate the level of phosphorus in your blood and to aid in the diagnosis of conditions known to cause abnormally high or low levels of phosphorus

When To Get Tested?

In follow up to an abnormal calcium level; when you have a kidney disorder or uncontrolled diabetes; when you are taking calcium or phosphate supplements

Sample Required?

A blood sample drawn from a vein in your arm or sometimes a timed urine collection (usually a 24-hour sample)

Test Preparation Needed?

Overnight fasting may be required for a blood sample; follow any instructions that you are given.

You may be able to find your test results on your laboratory's website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab's website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab's website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called "normal" values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits."

For more information, please read the article Reference Ranges and What They Mean.

What is being tested?

Phosphorus is a mineral that combines with other substances to form organic and inorganic phosphate compounds. The terms phosphorus and phosphate are often used interchangeably when talking about testing, but it is the amount of inorganic phosphate in the blood that is measured with a serum phosphorus/phosphate test.

Phosphates are vital for energy production, muscle and nerve function, and bone growth. They also play an important role as a buffer, helping to maintain the body's acid-base balance.

Phosphorus comes into the body through the diet. It is found in many foods and is readily absorbed by the intestines. About 70-80% of the body's phosphates combine with calcium to help form bones and teeth, another 10% are found in muscle, and about 1% is in nerve tissue. The rest is found within cells throughout the body, where they are mainly used to store energy.

Normally, only about 1% of total body phosphates are present in the blood. 

A wide variety of foods, such as beans, peas and nuts, cereals, dairy products, eggs, beef, chicken, and fish, contain significant amounts of phosphorus. The body maintains phosphorus/phosphate levels in the blood by regulating how much it absorbs from the intestines and how much it excretes via the kidneys. Phosphate levels are also affected by the interaction of parathyroid hormone (PTH), calcium, and vitamin D.

Phosphorus deficiencies (hypophosphatemia) may be seen with malnutrition, malabsorption, acid-base imbalances, hypercalcemia, and with disorders that affect kidney function. Phosphorus excesses (hyperphosphatemia) may be seen with increased intake of the mineral, hypocalcemia, and with kidney dysfunction.

Someone with a mild to moderate phosphorus deficiency often does not have any symptoms. With a severe phosphorus deficiency, symptoms may include muscle weakness and confusion. An extreme excess of phosphorus may cause symptoms that are similar to those seen with low calcium, including muscle cramps, confusion, and even seizures.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm. If a timed urine sample is required, you will be asked to save all of your urine over a set time period (usually 24 hours).

Is any test preparation needed to ensure the quality of the sample?

Overnight fasting may be required prior to collecting a blood sample; follow any instructions that you are given.

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Common Questions
  • How is it used?

    Phosphorus tests are most often ordered along with other tests, such as those for calcium, parathyroid hormone (PTH), and/or vitamin D, to help diagnose and/or monitor treatment of various conditions that cause calcium and phosphorus imbalances.

    While phosphorus tests are most commonly performed on blood samples, phosphorus is sometimes measured in urine samples to monitor its elimination by the kidneys.

  • When is it ordered?

    Since mildly abnormal phosphorus levels usually cause no symptoms, phosphorus testing is typically performed in follow up to an abnormal calcium test and/or when symptoms of abnormal calcium such as fatigue, muscle weakness, cramping, or bone problems are present.

    Phosphorus testing may also be ordered along with other tests when symptoms suggest kidney and gastrointestinal disorders.

    When conditions causing abnormal phosphorus and/or calcium levels are found, testing for both may be ordered at regular intervals to monitor treatment effectiveness.

    When someone has diabetes or signs of an acid-base imbalance, a health practitioner may sometimes monitor phosphorus levels.

  • What does the test result mean?

    Low levels of phosphorus (hypophosphatemia) in the blood may be due to or associated with:

    Higher than normal levels of phosphorus (hyperphosphatemia) in the blood may be due to or associated with:

  • Is there anything else I should know?

    Abnormally high levels of phosphorus can lead to organ damage due to calcification, deposits of calcium phosphate in the tissues. This is rare, however, and it is more common that high phosphorus levels lead to cardiovascular disease or osteoporosis.

    Phosphate levels are normally higher in children than in adults because their bones are actively growing. Low phosphate levels in children can inhibit bone growth and high levels may be an indication of a condition that disrupts the body's balance of minerals.

    Soft drinks and pre-packaged food items are high in phosphorus content, which some nutritionists believe contributes to over-consumption of phosphorus.

    Blood and urine levels of phosphorus may be affected by the use of enemas and laxatives containing sodium phosphate, excess dietary vitamin D supplements, and by intravenous glucose administration.

  • If there are no symptoms, how will I know if I have an abnormal phosphorus level?

    Abnormal phosphorus levels are usually detected because of the relationship with and effect on calcium levels. Calcium is routinely tested as part of the comprehensive metabolic panel (CMP) and basic metabolic panel (BMP), tests that are frequently ordered as part of a health exam. If you have an abnormal calcium level, your health care provider usually will check your phosphorus level.

  • Can vegetarians meet their phosphorus needs without resorting to meat or dairy?
    Yes, but only about 50% of the phosphorus in plant sources such as beans, lentils, grains, peanuts and almonds is available to the body because we lack the enzymes to process it. An exception to this is yeast breads because yeast provides the necessary enzyme.
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Related Content

On This Site

Tests: Calcium; Electrolytes; Vitamin D; PTH; Magnesium

Conditions: Kidney Disease, Diabetes, Acidosis and Alkalosis

Elsewhere On The Web

The Linus Pauling Institute: Phosphorus
Mayo Clinic: Phosphate supplement
Vitaguide.org: Phosphorus

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View Sources

Sources Used in Current Review

Holm, Gretchen. (Published June 1, 2012.) Serum Phosphorus Test. HealthLine.com. Available online at http://www.healthline.com/health/serum-phosphorus through http://www.healthline.com. Accessed October 2013.

Blood Test: Phosphorus. (Updated March 2011.) KidsHealth.org. Available online at http://kidshealth.org/parent/system/medical/test_phosphorus.html through http://kidshealth.org. Accessed October 2013.

Phosphorus - blood. MedlinePlus Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003478.htm. Accessed December 2013.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

Cohen, D. [Updated] (2002 February 15, Updated). Kidney diet - dialysis patients. MEDLINEplus [On-line information]. Availableonline at http://www.nlm.nih.gov/medlineplus/ency/article/007135.htm.

Zangwill, M. [Updated] (2001 February 02). Phosphorus in diet. MEDLINEplus [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/002424.htm.

Knochel, J. [Reviewed] (2001 January 10). Phosphorus. The Linus Pauling Institute [On-line information]. Available online at http://lpi.orst.edu/infocenter/minerals/phosphorus/.

Merck. Phosphate Metabolism. The Merck Manual of Diagnosis and Therapy [On-line information]. Available online at http://www.merck.com/pubs/mmanual/section2/chapter12/12e.htm through http://www.merck.com.

Spengler, R. (2000, November 16, Updated). Phosphate in Blood. WebMDHealth [On-line information]. Available online at http://my.webmd.com/encyclopedia/article/1821.50805 through http://my.webmd.com.

Spengler, R. (2000, November 16, Updated). Phosphate in Urine. WebMDHealth [On-line information]. Available online at http://my.webmd.com/encyclopedia/article/1821.50999 through http://my.webmd.com.

Dugdale, D. (Updated 2009 November 15). Serum Phosphorus. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003478.htm. Accessed March 2010.

Patterson, L. and DeBlieux, P. (Updated 2009 December 3). Hyperphosphatemia. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/767010-overview through http://emedicine.medscape.com. Accessed March 2010.

Moore, D. and Rosh, A. (Updated 2009 September 22). Hypophosphatemia. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/767955-overview through http://emedicine.medscape.com. Accessed March 2010.

Pagana, K. D. & Pagana, T. J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 722-723.

Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 852-855.

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