The kidneys are bean-shaped organs tucked under your ribcage in your back. They have important functions which help to keep your body healthy, removing harmful chemicals that affect how your organs work.

As blood flows into the kidney, it passes through ‘filters’ called nephrons (Figure 1). The nephrons remove proteins, nutrients, some water and some salts (sodium and potassium) from the blood and return it to the body. The nephrons also filter some water and chemical waste from the blood, and these are removed from the body as urine.

The kidney has many other vital roles, including:

• controlling blood pressure
• stimulating the production of new red blood cells
• activating vitamin D
• controlling calcium and phosphate levels in the blood and bone

Figure 1. The kidney.

Kidney disease

What is chronic kidney disease?

In chronic kidney disease (CKD), the nephrons in the kidney gradually lose their ability to filter the blood. CKD is classified into five stages, and the last is end-stage renal disease (ESRD) or stage 5. By the time a patient has ESRD, their kidneys are working about 90% less effectively than healthy kidneys, and dialysis (a mechanical process that does the job of a healthy kidney) is needed.1

Many people do not show any symptoms of CKD until the later stages of the disease. However, you may notice early symptoms, such as tiredness, itchiness, drowsiness, loss of appetite, loss of concentration or a change in how often you urinate. These symptoms are likely to worsen unless you visit your doctor. If you do not visit your doctor, you may be at risk of anaemia or hyperphosphataemia (too much phosphate in the blood).1 These symptoms may be dangerous as they are linked to problems with the heart, arteries and bone.1,2

How is kidney disease managed?

The aim of treatment is to slow the loss of kidney function, and to stop serious health problems by making up for the reduced function. In the earlier stages of CKD, your doctor may ask you to visit a renal dietician who specialises in patients with kidney disease, and to eat less protein, cholesterol and salts/minerals. A kidney transplant is often the best long-term treatment for severe CKD. However, until a transplant can be performed or until a replacement kidney is available, dialysis is normally used to make up for the loss in kidney function. There are two main types of dialysis:

• haemodialysis – a mechanical process that does the job of a healthy kidney, and that usually takes place in a hospital
• peritoneal dialysis – a process where the abdomen is filled with a fluid (‘dialysate’) through a plastic tube, and drained after waste has entered the fluid. This type of dialysis can be carried out at home or at work.

When you are on dialysis you may need other treatments, such as:

• drugs to control your blood pressure
• replacement erythropoietin (a hormone that stimulates your bone marrow to produce new blood cells and that the kidney loses the ability to produce in CKD)
• calcium, iron and other nutritional supplements
• phosphate binders to prevent the build up of phosphate in your blood
• faeces softeners and laxatives to manage constipation.

Dialysis can worsen the changes in electrolyte levels already caused by kidney disease, which means that levels of potassium, calcium, magnesium, and other important chemicals (‘electrolytes’) might change and the body will have difficulty regulating itself. These changes can cause an irregular heartbeat, and may eventually increase the risk of a heart attack.3

Focus on phosphate

In CKD, the normal balances between phosphate and calcium levels are changed as your kidneys lose their ability to:

• get rid of excess phosphate
• activate vitamin D to control calcium levels, which in turn affects phosphate.

Neither haemodialysis nor peritoneal dialysis are completely effective at removing phosphate. Changes to your diet will probably be necessary, but this may not be enough as you may still have too much phosphate even if the amount in your food is reduced. To deal with this, your doctor may prescribe a phosphate binder, a drug which removes phosphorus from the stomach after you have eaten and before it enters the blood. Phosphate binders are usually taken with meals.

Commonly used phosphate binders are calcium acetate, calcium carbonate, sevelamer and lanthamum carbonate. Calcium-based tablets can increase blood calcium levels so your doctor will tell you how many to take, although it is usually necessary to take several tablets. Calcium tablets have to be chewed and may leave a chalky taste in the mouth. You may experience constipation with calcium tablets or diarrhoea or nausea with any of these agents.

You will also have to continue to keep phosphate low in the diet, as phosphate binders can bind only a limited amount of phosphate.

References

1. Johnson CA, Levey AS, Coresh J et al. Clinical practice guidelines for chronic kidney disease in adults: Part I. Definition, disease stages, evaluation, treatment, and risk factors. Am Fam Physician. 2004;70:869-76.
2. Tonelli M, Wiebe N, Culleton B et al. Chronic kidney disease and mortality risk: a systematic review. J Am Soc Nephrol. 2006;17:2034-47.
3. Foley RN, Parfrey PS, Harnett JD, Kent GM, Hu L, O’Dea R, Murray DC, Barre PE: Hypocalcemia, morbidity, and mortality in end-stage renal disease. Am J Nephrol 16:386-393, 1996
4. Malluche HH, Monier-Faugere MC. Understanding and managing hyperphosphatemia in patients with chronic renal disease. Clin Nephrol. 1999;52:267-77.