Blood test

Normal phosphorus level in the blood

Blood test
Normal phosphorus level in the blood
Last update: 18/03/2020

What is the normal level of phosphorus in the blood?

Adults: 2.5-4.5 mg/dl
Children: 4-7 mg/dl

In the International System of Units (SI), phosphorus in the blood is measured in mmol/l. The normal blood phosphorus levels in the SI are:

Adults: 0.81-1.45 mmol/L
Children: 1.29-2.26 mmol/L

Why normal levels can differ across different labs?

Each laboratory must establish its own normal ranges for phosphorus in the blood. These ranges depend on the makeup of the local population, the technologies used and the accuracy of the measurement. There may be also slight differences in the normal levels according to age, gender, race or ethnic origin, geographic region, diet, type of sample and other relevant status.

Your doctor will study the results along with your medical record, screenings, physical condition, symptoms and any other relevant information about your situation.

In addition, when studying phosphorus levels in the blood it is important to keep in mind that:

  • Phosphorus presents in the blood may be higher during the healing of fractures.
  • Phosphorus level in the blood is lowest in the morning, experiment a rise in the early afternoon and a peak at night.

What is the role of phosphorus?

Phosphorus and calcium are essential for bone development. As much as 85% of all phosphorus in the body is found in the bones and teeth. Phosphorus is also present in the blood and it is necessary to help nerve function and to make muscles contract.

Phosphorus in the blood can be found bound to proteins (10%), linked to other ions like sodium, calcium or magnesium (35%) or in a free form (about 55%).

The terms phosphorus in the blood or phosphate in the blood are often interchangeable. Phosphorus is a mineral that combines with other substances to form organic or inorganic compounds called phosphates. In a routine blood test only inorganic phosphates are measured.

Phosphorus level in the blood depends on:

  • Phosphorus intake and its intestinal absorption
  • Kidney filtration
  • Parathyroid glands function
  • Vitamin D
  • Bone metabolism

What is a phosphorus blood test used for?

The phosphorus blood test is used to evaluate:

  • Kidney health
  • Parathyroid gland function (in case of suspected hypoparathyroidism or hyperparathyroidism)
  • Bone problems

Phosphorus values must be studied along with calcium levels in the blood. It is also interesting in some cases to test the phosphorus present in the urine.

Phosphorus is acquired by daily intake and assimilated trough intestinal absorption. Phosphorus is filtered by the kidneys of which 80-90% is reabsorbed and the remainder is excreted in the urine. Parathyroid hormone (PTH) regulates the reabsorption of phosphate in the kidneys.

Phosphorus or phosphate high levels may be a sign of kidney disease due to the kidneys are unable to filtrate and excrete the phosphorus excess.

Phosphorus or phosphate low levels in the blood can be found in case of:

  • An abnormally high phosphorus urine excretion
  • Intestinal absorption problems
  • Dysfunction of parathyroid gland (usually with high calcium levels in the blood)

Where can I find more information about phosphorus in the blood?

You can visit our pages about:

Which values are considered a normal phosphorus level in the blood?

The following values are considered to be normal values:

IMPORTANT: These levels are expressed in mg/dl. They are an example of a healthy man of about 45 years of age with no known disease, not taking any medication and with an appropriate intake of phosphorus in the diet. The ranges can be different depending on the laboratory or on your personal circumstances.

2.5 mg/dL2.6 mg/dL2.7 mg/dL2.8 mg/dL2.9 mg/dL3 mg/dL3.1 mg/dL3.2 mg/dL
3.3 mg/dL3.4 mg/dL3.5 mg/dL3.6 mg/dL3.7 mg/dL3.8 mg/dL3.9 mg/dL4 mg/dL
4.1 mg/dL4.2 mg/dL4.3 mg/dL4.4 mg/dL4.5 mg/dL   
Medically reviewed by Javier Muga Bustamante Ph.D. on 18/03/2020


  • Concise Book of Medical Laboratory Technology: Methods and Interpretations. 2nd Edition. 2015. Ramnik Sood. ISBN: 978-93-5152-333-8. Pag. 497.
  • Tietz. Fundamentals of Clinical Chemistry. Carl A. Burtis, Edward R. Ashwood, David E. Bruns, Barbara G. Sawyer. WB Saunders Company, 2008. Pag 717. ISBN: 978-0-7216-3865-2.
  • Common Terminology Criteria for Adverse Events (CTCAE). Version 4.0.Published: May 28, 2009. U.S. Department of health and human Services. Available on:
  • Fraser D, Jones G, Kooh SW, Radde IC. Calcium and phosphate metabolism. In: Tietz NW, ed. Fundamentals of clinical chemistry. Philadelphia:WB Saunders Company, 1987:706pp.

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