The main job of the kidneys is to remove waste from the blood and return the cleaned blood back to the body. Kidney failure means the kidneys are no longer able to remove waste and maintain the level of fluid and salts that the body needs.
One cause of kidney failure is diabetes mellitus, a condition characterised by high blood glucose (sugar) levels. Over time, the high levels of sugar in the blood damage the millions of tiny filtering units within each kidney.
This eventually leads to kidney failure.
Around 20 to 30 per cent of people with diabetes develop kidney disease (diabetic nephropathy), although not all of these will progress to kidney failure.
A person with diabetes is susceptible to nephropathy whether they use insulin or not. The risk is related to the length of time the person has diabetes.
There is no cure for diabetic nephropathy, and treatment is lifelong. Another name for the condition is diabetic glomerulosclerosis.
People with diabetes are also at risk of other kidney problems, including narrowing of the arteries to the kidneys, called renal artery stenosis or renovascular disease.
Symptoms of kidney failure
For people with diabetes, kidney problems are usually picked up during a check-up by their doctor. Occasionally, a person can have type 2 diabetes without knowing it.
This means their unchecked high blood sugar levels may be slowly damaging their kidneys. At first, the only sign is high protein levels in the urine, but this has no symptoms.
It may be years before the kidneys are damaged severely enough to cause symptoms. Some of the symptoms may include:
- Fluid retention (oedema of the legs or face)
The human body has two kidneys, one on either side of the spine beneath the lower ribs. Inside each kidney are about one million tiny units called nephrons.
Each nephron consists of a small filter (glomerulus) attached to a tubule. Water that contains waste is separated from the blood by the filters and directed into the tubules. Much of the water is returned to the blood by the tubules, while the wastes are concentrated into urine.
The urine is collected from the tubules by a funnel-like structure (renal pelvis). From there, the urine flows down a tube (ureter) that joins each kidney to the bladder.
Urine leaves the bladder via the urethra, the thin tube that connects to the outside of the body.
Kidneys affected by diabetic nephropathy no longer work efficiently, and trace amounts of protein appear in the urine (microalbuminuria).
The retained water and salts cause the characteristic fluid retention and, frequently, the blood pressure begins to rise.
How Does Diabetes Cause Kidney Disease?
When our bodies digest the protein we eat, the process creates waste products. In the kidneys, millions of tiny blood vessels (capillaries) with even tinier holes in them act as filters.
As blood flows through the blood vessels, small molecules such as waste products squeeze through the holes.
These waste products become part of the urine. Useful substances, such as protein and red blood cells, are too big to pass through the holes in the filter and stay in the blood.
Diabetes can damage this system. High levels of blood sugar make the kidneys filter too much blood. All this extra work is hard on the filters.
After many years, they start to leak and useful protein is lost in the urine. Having small amounts of protein in the urine is called microalbuminuria.
When kidney disease is diagnosed early, during microalbuminuria, several treatments may keep kidney disease from getting worse.
Having larger amounts of protein in the urine is called macroalbuminuria. When kidney disease is caught later during macroalbuminuria, end-stage renal disease, or ESRD, usually follows.
In time, the stress of overwork causes the kidneys to lose their filtering ability. Waste products then start to build up in the blood. Finally, the kidneys fail. This failure, ESRD, is very serious.
A person with ESRD needs to have a kidney transplant or to have the blood filtered by machine (dialysis).
How Can I Prevent It?
Diabetic kidney disease can be prevented by keeping blood sugar in your target range. Research has shown that tight blood sugar control reduces the risk of microalbuminuria by one third.
In people who already had microalbuminuria, the risk of progressing to macroalbuminuria was cut in half. Other studies have suggested that tight control can reverse microalbuminuria.
Treatments for Kidney Disease
Important treatments for kidney disease are tight control of blood glucose and blood pressure. Blood pressure has a dramatic effect on the rate at which the disease progresses.
Even a mild rise in blood pressure can quickly make kidney disease worsen. Four ways to lower your blood pressure are losing weight, eating less salt, avoiding alcohol and tobacco, and getting regular exercise.
When these methods fail, certain medicines may be able to lower blood pressure. There are several kinds of blood pressure drugs, however, not all are equally good for people with diabetes.
Some raise blood sugar levels or mask some of the symptoms of low blood sugar. Doctors usually prefer people with diabetes to take blood pressure drugs called ACE inhibitors.
ACE inhibitors are recommended for most people with diabetes, high blood pressure and kidney disease.
Recent studies suggest that ACE inhibitors, which include captopril and enalapril, slow kidney disease in addition to lowering blood pressure. In fact, these drugs are helpful even in people who do not have high blood pressure.
Another treatment some doctors use with macroalbuminuria is a low-protein diet. Protein seems to increase how hard the kidneys must work.
A low-protein diet can decrease protein loss in the urine and increase protein levels in the blood. Never start a low-protein diet without talking to your health care team.
Once kidneys fail, dialysis is necessary. The person must choose whether to continue with dialysis or to get a kidney transplant.
This choice should be made as a team effort. The team should include the doctor and diabetes educator, a nephrologist (kidney doctor), a kidney transplant surgeon, a social worker, and a psychologist.