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Hyperphosphatemia (High Level of Phosphate in the Blood)

by James L. Lewis, III, MD

In hyperphosphatemia, the level of phosphate in blood is too high.

Hyperphosphatemia is rare except in people with severe kidney dysfunction. In these people, the kidneys do not excrete enough phosphate (see Overview of Phosphate). Dialysis, often used to treat kidney dysfunction, is not very effective at removing phosphate and thus does not reduce the risk of hyperphosphatemia.

Less commonly, hyperphosphatemia develops in people with the following:

  • A low level of parathyroid hormone (hypoparathyroidism)

  • Lack of response to a normal level of parathyroid hormone (pseudohypoparathyroidism)

  • Diabetic ketoacidosis

  • Impaired kidney function or hemodialysis

  • Crush injuries

  • Destruction of muscle tissue (rhabdomyolysis)

  • Severe bodywide infections

  • Large amounts of phosphate taken by mouth or given in an enema

Most people with hyperphosphatemia do not have symptoms. However, in people with severe kidney dysfunction, calcium combines with phosphate, which lowers calcium levels in the blood (see Hypocalcemia (Low Level of Calcium in the Blood)). Low calcium can cause muscle cramps and spasms but also causes an increase in parathyroid hormone levels, resulting in bone weakness and other problems. The calcium and phosphate also can form crystals (calcify) in body tissue, including within the walls of the blood vessels. Severe arteriosclerosis (hardening of the arteries) can result, leading to strokes, heart attacks, and poor circulation. Crystals can also form in the skin, where they cause severe itching.

Diagnosis and Treatment

The diagnosis is based on blood tests indicating that the phosphate level is high.

Hyperphosphatemia in people with kidney dysfunction is treated by reducing consumption of phosphate and reducing absorption of phosphate from the digestive tract. Foods that are high in phosphate, such as milk, egg yolks, chocolate, and soft drinks, should be avoided. Drugs that bind with phosphate, such as sevelamer, lanthanum, and calcium compounds, should be taken with meals as prescribed by a doctor. By binding with phosphate, these drugs make it harder to absorb, and more phosphate is excreted. Sevelamer and lanthanum are often used for people undergoing dialysis because calcium compounds can make calcium-phosphate crystals more likely to form in tissues.

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