Le phosphorus is a mineral essential to many cellular reactions, in particular to the energy mechanisms of muscle cells. Phosphorus also plays a role in mineralization of bone tissue, just like the calcium.

About 85% of phosphorus is incorporated into the bones. Blood phosphorus, which is found in the form of monosodium or disodium phosphate, in particular, represents only 1% of total phosphorus.

Several factors are involved in the regulation of phosphorus levels in the blood (phosphorémie), of which :

• vitamin D level (increases digestive absorption)
• parathyroid hormone (increases digestive absorption and renal excretion)
• growth hormone (increases digestive absorption)
• corticosteroids (increase excretion)

The blood phosphorus dosage is indicated in case of bone disorders or in hospitalized people, in whom phosphoremia disorders are frequent.

This dosage of phosphorus is always associated with that of calcium (calcemia) and some creatinine (serum creatinine).

Indeed, the determination of the calcium level will allow the doctor to detect a hyperparathyroïdie (which also causes an increase in serum calcium).

Le dosage phosphorus is obtained from a blood sample, by a venipuncture usually at the crease of the elbow.

Urinary dosage (phosphaturie) is also possible: in this case, all urine must be collected over 24 hours. This dosage may be required in case of kidney disorders, suspected disorders of the parathyroid glands and of course bone disorders.

It is often indicated when the results of the blood test indicate low phosphoremia, to refine the diagnosis.

As a guide, normal blood phosphorus concentrations are between 0,8 and 1,5 mmol / L or 25 and 45 mg / L. In children, they are between 1,5 and 2 mmol / L.

A decrease in the level of phosphorus in the blood is called hypophosphatemia ; an increase is called hyperphosphorémie.

When blood and urine phosphorus is low (phosphaturia less than 10 mmoL / 24 h), hypophosphatemia is most often linked to a digestive problem: malabsorption, taking of antacids, chronic alcoholism.

When, on the contrary, the phosphaturia is high, it is possible that the person suffers from phosphorus or phosphate diabetes (loss of phosphorus in the urine). Further examinations will then be necessary.

Hypophosphatemia is common in hospitalized patients (1 to 3%) and particularly in those in intensive care (30 to 40%).

Hyperphosphatemia, on the other hand, is a possible complication of chronic renal failure. Since abnormalities in blood phosphorus levels can lead to various cardiac, respiratory or muscle complications, it is important to detect and treat them quickly.