Phosphate

Phosphorus is present in the body almost exclusively in the form of phosphate. Most of the body's phosphate is contained in bone. The rest is located primarily inside the cells, where it is involved in energy metabolism. Phosphate is necessary for the formation of bone and teeth. Phosphate is also used as a building block for several important substances, including those used by the cell for energy and DNA (deoxyribonucleic acid). Phosphate is taken in from the diet and excreted in urine and stool.

Hypophosphatemia

In hypophosphatemia, the level of phosphate in the blood is too low. Chronic hypophosphatemia occurs in people who have hyperparathyroidism, hypothyroidism (an underactive thyroid gland), or impaired kidney function or who use diuretics for a long time. Taking large amounts of aluminum-containing antacids for a long time or large amounts of the drug theophylline can also deplete the body's stores of phosphate. Phosphate stores are depleted in people with severe undernutrition, diabetic ketoacidosis, severe alcohol intoxication, or severe burns. The level of phosphate in the blood can fall dangerously low very quickly in people recovering from these conditions, because the body uses large amounts of phosphate during recovery.

Symptoms occur only when the phosphate level in the blood falls very low. Muscle weakness progresses to stupor, coma, and death. With prolonged mild hypophosphatemia, the bones can weaken, resulting in bone pain and fractures. The diagnosis is made by determining that the phosphate level in the blood is low.

Drinking one quart of low-fat or skim milk, which provides a large amount of phosphate, may help. A person with mild hypophosphatemia and no symptoms can take phosphate by mouth, but doing so usually causes diarrhea. If hypophosphatemia is very severe or if phosphate cannot be taken by mouth, intravenous phosphate may be given.

Hyperphosphatemia

In hyperphosphatemia, the level of phosphate in the blood is too high. Hyperphosphatemia rarely occurs except in people with severe kidney dysfunction. Dialysis is not very effective at removing phosphate.

Hyperphosphatemia rarely causes symptoms. Progressive bone weakness can occur, resulting in pain and increased susceptibility to fractures. Calcium and phosphate can crystallize in the walls of the blood vessels and heart, causing severe arteriosclerosis (hardening of the arteries) and leading to strokes, heart attacks, and poor circulation. Crystals can also form in the skin, where they cause severe itching. The diagnosis is made by determining that the phosphate level in the blood is high.

Hyperphosphatemia in people with kidney damage is treated by decreasing phosphate intake and reducing the absorption of phosphate from the digestive tract. Foods that are high in phosphate should be avoided. Phosphate-binding antacids should be taken with meals as prescribed by a doctor. These antacids bind to the phosphate and prevent it from being absorbed.