Phosphorus
- Also Known As:
- P
- PO4
- Phosphate
- Formal Name:
- Inorganic Phosphate
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.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 is obtained by inserting a needle into a vein in your 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).
Test Preparation Needed?
Overnight fasting may be required prior to collecting a blood sample; follow any instructions that you are given.
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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.
We get the phosphorus we need through the foods we eat. It is found in many foods and is readily absorbed by the digestive tract. Most of the body’s phosphates combine with calcium to help form bones and teeth. Smaller amounts are found in muscle and 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, increased blood calcium, and with disorders that affect kidney function. Phosphorus excesses (hyperphosphatemia) may be seen with increased intake of the mineral, low blood calcium, 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.
Common Questions
View Sources
Sources Used in Current Review
(© 1995–2018). Phosphorus (Inorganic), Serum. Mayo Clinic Mayo Medical Laboratories. Available online at https://www.mayomedicallaboratories.com/test-catalog/Overview/8408. Accessed on 3/18/18.
Markin, L. et. al. (2015 November 1, Updated). Phosphorous. MedlinePlus Medical Encyclopedia. Available online at https://medlineplus.gov/ency/article/003478.htm. Accessed on 3/18/18.
Suki, W. and Moore, L. (2016 Oct-Dec). Phosphorus Regulation in Chronic Kidney Disease. Methodist Debakey Cardiovasc J. 2016 Oct-Dec; 12(4 Suppl): 6–9. Available online at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5347182/. Accessed on 3/18/18.
Chang, A. and Anderson, C. (2017 August 21). Dietary Phosphorus Intake and the Kidney. Annu Rev Nutr. 2017 Aug 21; 37: 321–346. Available online at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5686387/. Accessed on 3/18/18.
Genzen, J. and Straseski, J. (2018 March, Updated). Hypercalcemia. ARUP Consult. Available online at https://arupconsult.com/content/hypercalcemia. Accessed on 3/18/18.
Hirsch, L. (2018 January, Reviewed). Blood Test: Phosphorus. KidsHealth from Nemours. Available online at https://kidshealth.org/en/parents/test-phosphorus.html. Accessed on 3/18/18.
Sofronescu, A. (2015 March 16, Updated). Phosphate (Phosphorus). Medscape Laboratory Medicine. Available online at https://emedicine.medscape.com/article/2090666-overview Accessed on 3/18/18.
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.
Spengler, R. (2000, November 16, Updated). Phosphate in Blood. WebMDHealth [On-line information]. Available online at http://my.webmd.com/encyclopedia/article/1821.50805.
Spengler, R. (2000, November 16, Updated). Phosphate in Urine. WebMDHealth [On-line information]. Available online at http://my.webmd.com/encyclopedia/article/1821.50999.
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. 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. 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.
Holm, Gretchen. (Published June 1, 2012.) Serum Phosphorus Test. HealthLine.com. Available online at http://www.healthline.com/health/serum-phosphorus. Accessed October 2013.
Blood Test: Phosphorus. (Updated March 2011.) KidsHealth.org. Available online at http://kidshealth.org/parent/system/medical/test_phosphorus.html. Accessed October 2013.
Phosphorus – blood. MedlinePlus Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003478.htm. Accessed December 2013.
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