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Overview of Disorders of Phosphate Concentration

By James L. Lewis, III, MD, Attending Physician, Brookwood Baptist Health and Saint Vincent’s Ascension Health, Birmingham

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Phosphorus is one of the most abundant elements in the human body. Most phosphorus in the body is complexed with oxygen as phosphate.

About 85% of the about 500 to 700 g of phosphate in the body is contained in bone, where it is an important constituent of crystalline hydroxyapatite. In soft tissues, phosphate is mainly found in the intracellular compartment as an integral component of several organic compounds, including nucleic acids and cell membrane phospholipids.

Phosphate is also involved in aerobic and anaerobic energy metabolism. RBC 2,3-diphosphoglycerate (2,3-DPG) plays a crucial role in oxygen delivery to tissue. Adenosinediphosphate (ADP) and ATP contain phosphate and use chemical bonds between phosphate groups to store energy.

Phosphate is a major intracellular anion but is also present in plasma.

The normal serum phosphate concentration in adults ranges from 2.5 to 4.5 mg/dL (0.81 to 1.45 mmol/L). Phosphate concentration is 50% higher in infants and 30% higher in children, possibly because of the important roles the phosphate-dependent processes play in growth.

Phosphate concentration can become

  • Too high (hyperphosphatemia), usually as a result of chronic kidney disease, hypoparathyroidism, and metabolic or respiratory acidosis

  • Too low (hypophosphatemia), usually as a result of alcoholism, burns, starvation, or diuretic use

The typical American diet contains about 800 to 1500 mg of phosphate. The amount in stool varies depending on the amount of phosphate-binding compounds (mainly calcium) in the diet. Also, like calcium, GI phosphate absorption is enhanced by vitamin D. Renal phosphate excretion roughly equals GI absorption to maintain phosphate balance. Phosphate depletion can occur in various disorders and normally results in conservation of phosphate by the kidneys. Phosphate in bone serves as a reservoir, which can buffer changes in plasma and intracellular phosphate.

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