Diabetic Nephropathy (Diabetic kidney disease) is a complication that occurs in some people with diabetes. In this condition the filters of the kidneys, the glomeruli, become damaged.
Because of this the kidneys leak abnormal amounts of protein from the blood into the urine. The main protein that leaks out from the damaged kidneys is called albumin.
In normal healthy kidneys only a tiny amount of albumin is found in the urine. A raised level of albumin in the urine is the typical first sign that the kidneys have become damaged by diabetes.
Diabetic kidney disease is divided into two main categories, depending on how much albumin is lost through the kidneys:
In this condition, the amount of albumin that leaks into the urine is between 30 and 300 mg per day. It is sometimes call incipient nephropathy.
In this condition the amount of albumin that leaks into the urine is more than 300 mg per day. It is sometimes call macroalbuminuria or overt nephropathy.
How does diabetic kidney disease develop and progress?
A raised blood sugar (glucose) level that occurs in people with diabetes can cause a rise in the level of some chemicals within the kidney. These chemicals tend to make the glomeruli more leaky which then allows albumin to leak into the urine.
In addition, the raised blood glucose level may cause some proteins in the glomeruli to link together. These cross-linked proteins can trigger a localised scarring process.
This scarring process in the glomeruli is call glomerulosclerosis. It usually takes several years for glomerulosclerosis to develop and it only happens in some people with diabetes.
As the condition becomes worse, scarred tissue (glomerulosclerosis) gradually replaces healthy kidney tissue. As a result, the kidneys become less and less able to do their job of filtering the blood.
Where the amount of albumin that leaks into the urine is between 30 and 300 mg per day – is usually the first sign that diabetic kidney disease has developed. Over months or years, microalbuminuria may go away (especially if treated – see below), persist at about the same level, or progress to proteinuria.
Where the amount of albumin that leaks into the urine is more than 300 mg per day – is irreversible. If you develop proteinuria it usually marks the beginning of a gradual decline in kidney function towards end-stage kidney failure at some time in the future.
How common is diabetic kidney disease?
Although diabetic kidney disease is more common in people with type 1 diabetes, there are more people with type 2 diabetes and diabetic kidney disease. This is because type 2 diabetes is much more common than type 1 diabetes.
Diabetic kidney disease is actually the most common cause of kidney failure. Around one in five people needing dialysis have diabetic kidney disease.
Note: most people with diabetes do not need dialysis.
For people with type 1 diabetes:
Microalbuminuria or proteinuria (defined above) is rarely present at the time when the diabetes is first diagnosed. By five years after the diagnosis of diabetes, about 14 in 100 people will have developed microalbuminuria.
After 30 years, about 40 in 100 people will have developed microalbuminuria. Some people with microalbuminuria progress to proteinuria and kidney failure.
For people with type 2 diabetes:
At the time the diabetes is first diagnosed, about 12 in 100 people have microalbuminuria and 2 in 100 have proteinuria. This is not because diabetic kidney disease happens straightaway in some cases but because many people with type 2 diabetes do not have their diabetes diagnosed for quite some time after the disease had begun. Diabetic kidney disease is much more common in Asian and black people with diabetes than in white people.
What are the symptoms of diabetic kidney disease?
You are unlikely to have symptoms with early diabetic kidney disease – for example, if you just have microalbuminuria (defined above). Symptoms tend to develop when the kidney disease progresses. With more severe kidney disease, symptoms that may develop include:
- Difficulty thinking clearly.
- A poor appetite.
- Weight loss.
- Dry, itchy skin.
- Muscle cramps.
- Fluid retention which causes swollen feet and ankles.
- Puffiness around the eyes.
- Needing to pass urine more often than usual.
- Being pale due to anaemia.
- Feeling sick.
The standard routine urine test is to compare the amount of albumin with the amount of creatinine in a urine sample. This is call the albumin: creatinine ratio (ACR). Creatinine is a breakdown product of muscle.
A blood test can show how well the kidneys are working. The blood test measures the level of creatinine, which is normally cleared from the blood by the kidneys.
If your kidneys are not working properly, the level of creatinine in the blood goes up. An estimate of how well your kidneys are working can be made by taking into account the blood level of creatinine, your age and your sex. This estimate of kidney function is call the estimated glomerular filtration rate (eGFR).