Kidney School™—a program of Medical Education Institute, Inc.

Module 16—Long-term Effects of Dialysis

Calcium-phosphorus product

Your calcium-phosphorus product (Ca x P) is your blood calcium level times your blood phosphorus level. This result should be part of your monthly blood test results. The NKF KDOQI guidelines for people on dialysis say that your product should be less than 55. You can reach this with a lower calcium level, lower phosphorus, or both. The best thing you can do is keep phosphorus in the normal range.

When Crystals Attack! Extraskeletal Calcification & Calciphylaxis

A high calcium-phosphorus product means extra calcium and phosphorus are in your blood, where they can form crystals. You may find that you have bone where it doesn't belong. Extraskeletal calcification means bone is forming outside your skeleton. This can happen in your eyes, blood vessels, heart, lungs, or other organs. It may show up as knobs or lumps on top of bones, in joints or on tendons, etc. In some cases, a surgeon can remove these bone lumps to help improve function.

Worse, the crystals can harm blood vessels and even cut off blood flow to a finger or toe, a whole limb, or soft tissue. This problem—calciphylaxis—is painful and can be fatal. It occurs in about 4% of people on standard HD. It starts as red or purple skin marks (often on both arms or legs in the same spots). They may look like bruises. A skin biopsy shows calcium in the tissues. The marks turn black as the skin dies, and turns into ulcers that grow larger and won't heal. People with diabetes are at a higher risk. Treatment for calciphylaxis may include:

  • Phosphate binders – These help pull extra phosphorus out of the blood.
  • Antibiotics – It is vital to prevent infection in the skin ulcers.
  • Sodium thiosulfate – New studies have found that this drug, which pulls calcium out of the body, may be able to help. The drug is most often given in a vein, but may be given into the peritoneum.
  • Kidney transplant – A new kidney will remove more excess calcium and phosphorus from the blood.
  • Parathyroidectomy – Removing most of the parathyroid glands will change the balance of calcium and phosphorus in the body.
  • Hyperbaric oxygen chambers – Used for deep sea divers with "the bends," these chambers force oxygen into the tissues and can help heal skin ulcers. Not all hospitals have a hyperbaric oxygen chamber. To find one, put "hyperbaric oxygen chamber" and the name of your city and state into Google.
  • Amputation – If a problem in a limb is not healing, removing the limb may save your life.
Ca x P Calculator

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