Why Monitoring Phosphorus is Important

by A. Peter Lundin, MD and Maureen F. Lundin, RN

Editor's Note: This article was written in 1992. Most of the information in this article remains true today, however new treatments have emerged in the past nine years. If you have questions about phosphorus and bone disease, please consult your healthcare professional.

How can your bones just disappear? Well, they can't entirely. But they can get weak enough that they lose their function - supporting the body and bearing weight. Although there are a number of medical terms for this - osteodystrophy, osteomalacia, osteoporosis - it is generally called bone disease. If you suffer from kidney failure, you will be affected by it.

Everyone who is on dialysis therapy has been warned about watching calcium and phosphorus levels to prevent bone disease. Some of you may feel you are even being nagged by your doctor, nurses and dietitian about this. But do you have any clear idea of what bone disease is or what it can do to a person?

Why You Need To Be Concerned

The two worst cases of bone disease I have ever seen occurred in two of my fellow patients at Kings County Hospital in Brooklyn, in the pioneering days of hemodialysis treatment. All of us had some bone disease in those days, but even then it could be treated by modifying the diet and taking phosphate binders. These two, however, adamantly refused to do either. I think that they simply did not believe the warnings. They did not want to take the trouble and there was no obvious reason to do so. So without treatment, their bone disease progressed much more rapidly than did ours.

As they lost more and more bone calcium from their bones, these two unfortunates started getting shorter and more stooped as their spines curved. They began to suffer frequent broken bones, then constant broken bones. They became confined to wheelchairs. Eventually, they became bedridden and couldn't care for themselves at all. They were in constant pain. Their condition certainly contributed to their early deaths.

Today, we can greatly slow down the progression of bone disease and may be able to stop it altogether. It is a process that requires teamwork between the healthcare team and the patient. It is important for you to care for your bones even if you plan to receive a transplant. Some immunosuppressive drugs can also damage the bones, so it is important that your bones be in good shape before the transplant.

Losing calcium from the bones is a problem common to all dialysis patients. This loss happens over a long period of time, and may start well before you reach the stage of kidney failure when you will need dialysis or a transplant. It results in an ongoing weakening of the bones. If nothing is done to avert the calcium loss, you will eventually experience broken bones, and this can happen unexpectedly, as a result of very little force. Signs or symptoms you may notice before this happens are joint pains, curvature of the spine (kyphosis) and loss of height (with the loss of calcium from your spine). At a late stage in bone disease, you could end up like the two ill-fated people I described, weighing half your normal weight and unable to care for yourself.

What The Problem Is

An active form of Vitamin D, calcitriol, is made in the kidneys and specifically assists in your body's acquiring calcium from the food you eat. As kidney function becomes worse and dialysis is needed, a mineral in the blood called phosphorous becomes higher than normal. The extra phosphate circulates in the blood looking for calcium to bind with. Your body, lacking the controls on this process which are provided by a healthy working kidney, will take calcium from your bones if necessary to attach to the phosphate.

What You Can Do About It

First you want to get the phosphate levels in your blood under control. This is still done with a combination of diet and medication. Start by keeping your intake of phosphorous down. Check the list of foods high in phosphate (see table on this page) and check with your dietitian. Your phosphate levels can also be lowered by taking phosphate binders such as calcium acetate or calcium carbonate to lower the phosphate to a safe range.

Always take your phosphate binders with meals. They work by attaching themselves to molecules of phosphorus in the stomach and intestine, and holding them so they can be excreted in the stool. It defeats the whole purpose if they are not taken with food. Some binders, particularly the ones with aluminum, can even make you nauseous if taken on an empty stomach.

When the phosphate levels are adequate, then you can take calcitriol in a pill form, Rocaltrol, to get your blood calcium levels toward the upper normal range. If these levels become too high from the calcium phosphate binders, it may be necessary to add some containing aluminum. (Aluminum-containing binders were taken by all dialysis patients until recently, when the concern about aluminum being deposited in the bones prompted a switch to the calcium binders.) Check the alkaline phosphatase level on your monthly blood chemistries. It should be at a normal level. A rising alkaline phosphatase is a marker for bone (or in some cases, liver) disease.

Why These Recommendations Are Hard To Follow

There are four major reasons why it is hard to follow the above recommendations:

Phosphorus is present in many favorite foods. It can be difficult to deprive ourselves of something we like so much. Chocolate, eggs, nuts, and cola drinks are among the foods highest in phosphorus. So are dried beans, which are so much a part of the diet of those who come from the American South, the Caribbean and Latin America.
The phosphate binders can cause constipation. This is particularly true for those containing aluminum. Most people realize this fairly quickly, and all too frequently stop taking them. It is a normal response to not inflict discomfort on oneself, but in this case such a decision will cause you grief down the road. It is much easier to treat and prevent constipation than the loss of bone.
It is hard to remember to take the binders. Taking pills is, for most people, not a life-long, ingrained habit. The binders should be taken with meals and many of you may be away from home for one or more meals a day. Keep the pills at the table where you eat at home in a place where you can see them, perhaps laying them out next to your plate before you eat. For meals away from home put some in a pill case and carry them with you. New habits can be developed when one considers it necessary.
Taking the phosphate binders is more of a bother than not taking them. You may think this is true, but it is very shortsighted. The reality of getting bone disease and complications from loss of bone will only be felt a number of years from now. This has to be taken as a matter of trust. Maybe you also will meet or know of patients who experienced problems with their bones because they didn't follow these recommendations.

If You Already Have A Problem

What should you do if you have been on dialysis for a number of years, and weren't advised as to how to prevent bone disease or didn't follow the advice and now have the problems described above? After renal bone disease (osteodystrophy) develops, it can become very complicated. Further loss of calcium from the bone can still be halted by the use of intravenous calcitriol (Calcijex). Aluminum can be removed from the bone by a binding (chelating) substance called desferrioxamine (Desferal). Replacing the lost calcium in the bone remains a problem, however. If you are in this situation, ask your doctor to refer you to an expert in renal bone disease. In summary, the loss of calcium from your body can lead to bone weakness and fractures. The culprits are too little active vitamin D, and later too much phosphate in the blood. Use diet and phosphate binders to keep blood phosphate and calcium levels normal.

Believe that it will happen to you! Even if you plan on having a kidney transplant, it will be difficult to restore the calcium that you have already lost.

Editor's Note: We remind you once again, that new treatments have emerged since this article was written.

This article originally appeared in aakpRENALIFE 1992, Vol. 7, No. 2.