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Bones, Calcium, Phosphate, and PTH in Kidney Failure - Calciphylaxis

 
Introduction
Calciphylaxis and the heart
Calciphylaxis and blood vessels
Calciphylaxis and other tissues
How is calciphylaxis prevented?

Introduction

Calciphylaxis means the deposition of calcium and phosphate in parts of the body other than the bones. The calcium and phosphate form brittle, chalky material. In some cases it can resemble tissues of the body turning into bone. The chemical deposited is, strictly speaking, calcium phosphate, but it is often just referred to as calcium.

Severe calciphylaxis is rare but can have serious consequences. Kidney doctors are anxious to control the levels of calcium, phosphate and PTH to prevent severe calciphylaxis.

Calciphylaxis occurs at a faster rate when the levels of calcium and phosphate are high. Chemically, they come out of solution as calcium phosphate. The likelihood of the chemical reaction occurring depends on the levels of calcium and phosphate, and can be predicted by multiplying the blood levels together. The calcium-phosphate product should be less than 4.5. For example, if the calcium level is 2.89 mmol/l and the phosphate level is 2.24 mmol/l, the product is 2.89 mmol/l x 2.24 mmol/l = 6.47 - too high. If the calcium is 2.2 and the phosphate 1.75, the product is 2.2 x 1.75 = 3.85, in the acceptable range (note these examples will not apply in parts of the world where blood levels are measured in different units, such as the USA).

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Calciphylaxis and the heart

Calciphylaxis can occur in heart valves, causing them to become chalky and eventually to narrow. The aortic valve, which controls the flow of blood out of the heart into the body, can be particularly affected. In some people who have been on dialysis for many years, surgery to replace the valve may be needed. This is a major procedure with a significant complication and death rate.

Recent research has also shown that the arteries supplying the heart (coronary arteries) can develop calcium deposits. The significance of these is not clear. The calcium is deposited in the middle of the artery wall, and is not directly associated with the types of fatty narrowing that causes heart attacks. Further research is necessary to show whether these deposits are important. However, it seems that good phosphate control reduces their appearance

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Calciphylaxis and blood vessels

Blood vessels throughout the body can develop calcium deposits, and this can contribute to narrowing, leading to poor blood supply to the feet or other parts of the body. Diabetes and atherosclerosis (narrowing due to cholesterol) also cause narrowing, and all these factors can act together to cause poor blood supply.

Calciphylaxis and other tissues

In theory any tissue can develop calcium deposition, but often, even though calcium can be seen on an X-ray, it does not cause any medical problems.

How is calciphylaxis prevented?

All the measures discussed here together with diet, good dialysis, phosphate binders and parathyroidectomy when necessary will reduce the chances of development of calciphylaxis.

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The National Kidney Federation cannot accept responsibility for information provided. The above is for guidance only. Patients are advised to seek further information from their own doctor.

NKF Controlled Document No. 23: Calciphylaxis written:  last reviewed: 07/03/2019