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Inorganic phosphorus in the blood
Last reviewed: 05.07.2025
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Phosphorus in the body is contained in inorganic (calcium, magnesium, potassium and sodium phosphates) and organic (carbohydrates, lipids, nucleic acids, etc.) compounds. Phosphorus is necessary for bone formation and cellular energy metabolism. Approximately 85% of all phosphorus in the body is in the bones, most of the rest is inside the cells, and only 1% is in the extracellular fluid. Phosphates are the main intracellular anion. In the cellular elements of the blood, phosphorus is present only as part of organic compounds, and the blood serum mainly contains inorganic phosphates, the determination of the amount of which is of greatest interest to the clinician.
In addition to inorganic phosphorus, the concentration of which in serum and erythrocytes is almost the same, there is also a fraction of acid-soluble phosphorus and lipid phosphorus in the blood. About two-thirds of all acid-soluble phosphorus in the blood is part of 2,3-diphosphoglyceric acid, the amount of which increases in all diseases accompanied by hypoxia; the rest is represented by ATP and ADP phosphorus. Most of the lipid phosphorus is accounted for by phosphatidylcholines (lecithins) and phosphatidylethanolamines (cephalins). About 40% of the phosphorus not used by the body is excreted in feces, and the rest in urine.
Reference values (norm) of inorganic phosphorus concentration in blood serum
Age |
Serum phosphorus concentration |
|
Mg/dl |
Mmol/l |
|
24-48 h |
5.5-9.5 |
1.78-3.07 |
Up to 1 year |
4.5-6.5 |
1.45-2.10 |
Children |
4.5-5.5 |
1.45-1.78 |
Adults |
2.7-4.5 |
0.87-1.45 |
Over 60 years old: |
||
Men |
2.3-3.7 |
0.74-1.20 |
Women |
2.8-4.1 |
0.90-1.32 |
The role of phosphorus compounds is that they serve as a plastic material, participate in the regulation of acid-base balance and in various processes of carbohydrate, fat and protein metabolism. Phosphorus participates in the formation of nucleic acids, nucleotides, phospholipids and other compounds. A phosphorus concentration below 0.3 mmol/l leads to disruption of cellular energy metabolism.
The main factors regulating phosphorus metabolism are PTH, which reduces the concentration of phosphorus in the blood serum by activating its excretion by the kidneys; 1,25-dihydroxycholecalciferol, which increases it by activating phosphate absorption in the intestine; calcitonin, which has a hypophosphatemic effect; insulin, which reduces the concentration of phosphorus by stimulating its transfer into cells. Phosphorus metabolism in the body is closely related to calcium metabolism, so the quantitative ratio of calcium and inorganic phosphorus in the blood is of great diagnostic importance. Normally, this ratio in children is 1.9-2, and in rickets it increases to 3 and higher.
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