Bones, Calcium, Phosphate, and PTHin Kidney Failure
Bones, Calcium, Phosphate, and PTHin Kidney FailureThere are several types of treatment used. No single treatment is effective for all these problems, largely because dialysis cannot replace 100% of kidney function, and there is almost always a tendency to high phosphate levels.
A reduced phosphate diet will help you control the level in your blood. On a low phosphate diet the following foods should be limited but not avoided:
| FOOD | QUANTITY | ||||||
|---|---|---|---|---|---|---|---|
|
Milk |
½ pint/day
|
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|
Cheese |
No more than 1oz per day (Cream Cheese and Philadelphia are lower) |
||||||
|
Eggs |
No more than 1 per day. A maximum of 3-4 per week |
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|
Offal |
e.g. Heart, Liver, Kidney, Sweetbreads. No more than once per fortnight. |
You should also try to avoid the following foods:
Meat and fish do contain phosphate, but it is important not to limit these too much as they contain protein. If in doubt discuss this with your Dietitian. It is important that you continue to eat well.
If you are prescribed phosphate binders (e.g. Calcichew, Titralac, Alucaps, Phosex, Renagel) it is important that these are taken only with meals containing protein (e.g meat, fish, milk, cheese and eggs). These will help to bring your phosphate level down.
(Written by Caroline Dean, Dietitian, University Hospitals Coventry and Warwickshire, UK)
Good quality dialysis means more effective removal of waste products from the blood. This is very important because phosphate is not removed from the body very efficiently by dialysis. Therefore if the dialysis is not working well, there will be high levels of phosphate with all the problems that can arise from this (click here for more details on High Phosphate)
Therefore, whether treatment is being given with peritoneal dialysis or haemodialysis, there should be checks on the quality of dialysis every so often. If dialysis is not properly effective, it may be necessary to change the dialysis in some way, for example making haemodialysis sessions longer.
Unfortunately even good dialysis does not always remove enough phosphate. Therefore, it is always necessary to restrict phosphate levels in the diet, and it is usually necessary to take phosphate binding drugs.
Since deficiency of vitamin D is one of the main causes of calcium and bone problems in people with kidney diseases, vitamin D can be given as replacement treatment.
This is not quite so simple as it might sound, because vitamin D taken in food is not active. It needs to be converted to an active form, first in the skin by the effects of sunlight, and secondly in the kidneys. In severe kidney disease the final conversion step does not happen so that a special form of vitamin D has to be given which has already undergone this activation process.
The kidney stops converting vitamin D to its active form when down to about 40% of normal function. Anyone with kidney function down at this level should be considered for vitamin D replacement. However, if the blood calcium level is normal and the level of parathyroid hormone (PTH) is normal, vitamin D therapy is not always prescribed, as research has not shown universal benefits.
The type most commonly used is called ALFACALCIDOL which can be taken as a capsule - usually once a day in the morning. Side effects can include feeling sick - try taking it with food. Sometimes it is prescribed to be taken once or twice a week, in a bigger dose. Alfacalcidol is also available as an injection, and may be given after a session of haemodialysis.
An unwanted effect of alfacalcidol, when taken either as an injection or as a capsule, is that the level of calcium in the blood can go too high, so regular blood tests are necessary to monitor the blood calcium levels. Sometimes a person cannot taken alfacalcidol because of repeated high calcium levels. Click here for more details on the symptoms of high calcium levels.
Phosphate binders are a group of medicines which bind to phosphate in your food and prevent your body from absorbing the phosphate. They only work effectively in combination with controlling your diet (see diet section above).
Alucaps are a phosphate binder which contains aluminium. It is very effective at binding phosphate, but if taken over a long period of time, aluminium can build up in the body possibly causing memory problems. Side effects of Alucaps include constipation. Alucaps should be swallowed whole 10-15 minutes before meals.
Calcichew, Titralac and Phosex (calcium acetate) are phosphate binders which contain calcium. Side effects include a chalky taste in the mouth, or sometimes the level of calcium in your blood can rise. Calcichew and titralac tablets should be chewed, and Phosex should be swallowed whole, 10-15 minutes before meals
Sevelamer (Renagel) is a new type of phosphate binder. It does not contain calcium or aluminium. The capsules need to be swallowed whole with meals.
The dose you need to take of any of the above varies according to the phosphate level in your blood. You may need to take different numbers of tablets with each meal depending on how much phosphate is in the meal (see diet section).
Click here for more information on Phosphate Binders.
Unfortunately this does not put everything back to normal.
A successful kidney transplant is the best treatment for kidney failure, but it cannot reverse all the problems that have developed prior to the transplant. Even someone transplanted before they need dialysis may have some problems.
Usually, however, even though all the blood tests may not go completely back to normal after a kidney transplant, serious problems do not develop.
It is important to mention some problems that can occur:-
A class of drug has recently been developed which mimics the action of calcium, and may be useful in people on dialysis with severe PTH problems. The class of drug is called ‘calcimimetics’. The drug makes the body think there is more calcium in the blood than is actually the case. This reduces the production of excessive PTH. The blood calcium level can fall as a result, which is good if the blood calcium level is high. A reduction in the blood calcium level can also allow a higher dose of calcium-containing phosphate binders to be used to control the blood phosphate level, without at the same time causing a high blood calcium level.
The first drug in this class to become available in the UK is called Cinacalcet, with the trade name “Mimpara”. It can certainly reduce PTH levels in patients with very high PTH levels, and is therefore a possible alternative to an operation to remove overactive parathyroid glands. Calicimimetics offer the benefit of controlling PTH release from parathyroid glands without increasing calcium and phosphorus levels. It can cause mild to moderate nausea and sickness, but is generally easy to take. However, it is very expensive, and at present has not been approved for widespread use by the National Institute for Clinical Excellence (NICE). If it is used, it will be prescribed by the renal specialist and will require careful monitoring of the blood calcium and PTH levels.
NKF Controlled Document No. 20, Bones, Calcium, Phosphate, and PTH in Kidney Failure, written (date unknown). Last reviewed 27 October 2008.
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.
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Last updated: 29 April 2009