Diabetic nephropathy (diabetic kidney disease) is kidney damage that results from having diabetes.
Having high blood glucose levels due to diabetes can damage the part of the kidneys that filters your blood. The damaged filter becomes 'leaky' and lets protein into your urine.
For some people, diabetic nephropathy can progress to kidney failure. However, most people with diabetes do not develop kidney disease that progresses to kidney failure.
How common is diabetic nephropathy?
Diabetic nephropathy is common. One in 4 women and one in 5 men with type 2 diabetes develops diabetic nephropathy. It is even more common in type 1 diabetes.
Diabetic kidney disease is the leading cause of kidney failure in Australia.
Diabetic nephropathy usually has no symptoms early on. You can't tell that there is protein in your urine – it's something that is detected with a urine test.
It can take many years for the kidney damage to progress. Symptoms usually only appear when kidney damage has deteriorated significantly. Even then, the symptoms tend to be vague.
If the kidney damage becomes severe, you may notice:
- weight loss;
- a poor appetite or feeling sick;
- swollen ankles and feet (due to retaining fluid);
- puffiness around the eyes;
- dry, itchy skin;
- muscle cramps;
- needing to pass urine more often;
- feeling tired; and
- having difficulty concentrating.
What happens to the kidneys in diabetes?
The main function of the kidneys is to filter waste products and excess water from the bloodstream so that they can be excreted in the form of urine. This is carried out by a system of tubes and blood vessels known as nephrons. Inside the nephrons are tiny blood vessels called capillaries and tiny urine-collecting tubes. One of the major structures in the nephron is a group of blood vessels known as the glomerulus, which acts as a filter.
Having high blood glucose levels can interfere with the function of the glomerulus. The filtering function of the kidneys doesn't work properly and proteins start to leak from the blood into the urine.
High blood glucose levels can also cause scarring of the glomerulus (called glomerulosclerosis). As the scarring gets worse, the kidneys stop being able to filter waste products from the blood.
When enough glomeruli have been damaged, kidney failure results.
People who have diabetic nephropathy also often have high blood pressure. High blood pressure can further contribute to kidney damage.
Risk factors for diabetic nephropathy
There are many factors that can increase your risk of developing diabetic nephropathy. These include:
- having a family history of kidney disease;
- having high blood glucose levels (because your diabetes is not well managed);
- having high blood pressure;
- being overweight or obese; and
What are the complications?
The main complication of diabetic kidney disease is developing chronic kidney disease. Chronic kidney disease can progress even further to kidney failure. People with kidney failure need treatment with dialysis or a kidney transplant.
All people with diabetes are at risk of high blood pressure and cardiovascular disease (e.g. heart disease, stroke). Having kidney disease also increases the risk of these problems. So having both diabetes and kidney disease means your risk is even higher.
Tests and diagnosis
Your doctor will ask about any symptoms you have and perform a physical examination. The main tests done to check for evidence of diabetic nephropathy and how well your kidneys are functioning include a urine test and a blood test.
Urine samples are tested for a protein called albumin. The amount of albumin found in the urine indicates the amount of damage to your kidneys.
Microalbuminuria (tiny amounts of albumin in the urine) indicates that you are at risk of developing diabetic nephropathy or may have early stage diabetic nephropathy.
Proteinuria, or macroalbuminuria, (larger amounts of albumin in the urine) indicates that you have more advanced diabetic nephropathy that may be affecting the ability of your kidneys to filter wastes.
Blood tests are also recommended to check your kidney function. The level of creatinine, a waste product in the blood, can be measured to calculate your estimated glomerular filtration rate (eGFR). The eGFR gives an indication of how well the kidneys are working to filter waste products from your blood.
It is usually recommended that people with diabetes have blood and urine tests at least once a year to check on kidney function.
Treatment for diabetic nephropathy
Early detection and treatment of diabetic nephropathy can not only stop the progression of kidney disease in people with diabetes, but during the early stages can actually reverse it. Treatment involves controlling both your blood glucose levels and your blood pressure.
Blood glucose levels should be kept in the normal range as much as possible to prevent or slow the progression of diabetic nephropathy. Lifestyle measures (including diet and exercise) in combination with oral diabetes medicines (oral hypoglycaemics) or insulin can be used to control blood glucose levels.
People with type 2 diabetes who have microalbuminuria or proteinuria (evidence of of some degree of diabetic nephropathy) are usually also treated with medicines called angiotensin-converting enzyme inhibitors (ACE inhibitors) or angiotensin receptor blockers (ARBs). These medicines are also used to control blood pressure, but even if your blood pressure is normal, your doctor may prescribe an ACE inhibitor or ARB because they decrease the amount of protein in the urine and can prevent or slow the progression of diabetic kidney disease.
Other medicines may also be prescribed to help control high blood pressure.
Eating a healthy diet and getting regular physical activity are important in controlling your blood glucose levels and blood pressure. Your doctor and diabetes educator can provide you with advice about a healthy diet and exercise recommendations.
You may be advised to avoid high-protein diets if you have diabetic nephropathy, as excessive dietary protein may further damage the kidneys. A reduced-protein diet may be recommended for people with advanced diabetic nephropathy, to help delay the onset of kidney failure. You should never restrict major food groups from your diet without first checking with your doctor or diabetes educator.
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2. Shlipak M. Diabetic nephropathy. BMJ Clinical Evidence 2009; 01: 606