Diabetes and Kidney Disease Explained

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.

Understanding the kidneys and urine

Cross-section diagram of the urinary tract
The two kidneys lie to the sides of the upper part of the tummy (abdomen), behind the intestines, and either side of the spine. Each kidney is about the size of a large orange, but bean-shaped.

A large artery – the renal artery – takes blood to each kidney. The artery divides into many tiny blood vessels (capillaries) throughout the kidney. In the outer part of the kidneys, tiny blood vessels cluster together to form structures called glomeruli.

Each glomerulus is like a filter. The structure of the glomerulus allows waste products and some water and salt to pass from the blood into a tiny channel called a tubule whilst keeping blood cells and protein in the bloodstream.

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)
  • Fatigue
  • Headache
  • Nausea
  • Vomiting.
  • Kidneys explained

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.

What are the main functions of the kidneys?

The main functions of the kidneys are to:

  • Filter out waste products from the bloodstream to be passed out in the urine.
  • Help control blood pressure – partly by the amount of water passed out of the body as urine and partly by making hormones which are involved in blood pressure control.
  • Make a hormone called erythropoietin (‘epo’) which stimulates the bone marrow to make red blood cells. This is needed to prevent anaemia.
  • Help keep various salts and chemicals in the blood at the right level. For example, sodium, potassium, calcium, and phosphate. An imbalance of salts and chemicals in the bloodstream can cause problems in other parts of the body.

What is diabetic kidney disease?

Diabetic kidney disease (diabetic nephropathy) 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:

Microalbuminuria. This is when the amount of albumin that leaks into the urine is between 30 and 300 mg per day. It is sometimes called incipient nephropathy.
Proteinuria. This is when the amount of albumin that leaks into the urine is more than 300 mg per day. It is sometimes called 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 called glomerulosclerosis. It usually takes several years for glomerulosclerosis to develop and it only happens in some people with diabetes.

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 has diabetic kidney disease.

Note: most people with diabetes do not need dialysis.

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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.

Of those people who do not have any kidney problem when their diabetes is diagnosed, microalbuminuria develops in about 15 in 100 people, and proteinuria in 5 in 100 people, within five years.

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.

The symptoms at first tend to be vague and nonspecific, such as feeling tired, having less energy than usual, and just not feeling well. 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
  • As the kidney function declines then various other problems may develop. For example, anaemia and an imbalance of calcium, phosphate and other chemicals in the bloodstream. These can cause various symptoms, such as tiredness due to anaemia, and bone thinning or fractures due to calcium and phosphate imbalance.
  • End-stage renal failure is eventually fatal unless treated.

How is diabetic kidney disease diagnosed and assessed?

Diabetic kidney disease is diagnosed when the level of albumin in the urine is raised and there is no other obvious cause for this. Urine tests are part of the routine checks that are offered to people with diabetes from time to time. Urine tests can detect albumin (protein), and measure how much is present in the urine.

The standard routine urine test is to compare the amount of albumin with the amount of creatinine in a urine sample. This is called 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 called the estimated glomerular filtration rate (eGFR).

  • Proteinuria
  • Muscle Weakness
  • Mild-to-moderate Chronic Kidney Disease

What increases the risk of developing diabetic kidney disease?

All people with diabetes have a risk of developing diabetic kidney disease. However, a large research trial showed that there are certain factors that increase the risk of developing this condition. These are:

  • A poor control of your blood sugar (glucose) levels. (The greater your HbA1c level, the greater your risk.)
  • The length of time you have had diabetes.
  • The more overweight you become.
  • Having high blood pressure. The higher your blood pressure, the greater your risk.
  • If you are male.

This means that having a good control of your blood glucose level, keeping your weight in check and treating high blood pressure will reduce your risk of developing diabetic kidney disease.

If you have early diabetic kidney disease (microalbuminuria), the risk that the disease will become worse is increased with:

  • The poorer the control of blood sugar levels. (The greater your HbA1c level, the greater your risk.)
  • Having high blood pressure. The higher your blood pressure, the greater your risk.
  • Smoking.
  • What are the possible complications?
  • End-stage kidney failure

In people with proteinuria (described above), end-stage kidney failure develops in approximately 8 in 100 people after 10 years. If this occurs then you would need kidney dialysis or a kidney transplant.

Cardiovascular diseases

All people with diabetes have an increased risk of developing cardiovascular diseases, such as heart disease, stroke and peripheral vascular disease. If you have diabetes and diabetic kidney disease, then your risk of developing cardiovascular diseases is increased further.

The worse the kidney disease, the further increased the risk. This is why reducing any other cardiovascular risk factors is so important if you have diabetic kidney disease.

High blood pressure

Kidney disease has a tendency to increase blood pressure. In addition, increased blood pressure has a tendency to make kidney disease worse. Treatment of high blood pressure is one of the main treatments of diabetic kidney disease.

The mechanism is unknown

It is clear that diabetes can lead to kidney disease, but just why high blood sugars should damage the glomeruli is unclear. High blood pressure (hypertension) is a known risk factor for kidney disease and people with diabetes are prone to hypertension.

The renin-angiotensin system – which helps regulate blood pressure – is also thought to be involved in the development of diabetic nephropathy.

Other risk factors include cigarette smoking and family history. Diabetic nephropathy progresses steadily despite medical intervention. However, treatment can significantly slow the rate of damage.

Diagnosis methods

  • Diabetic nephropathy is diagnosed using a number of tests including:
    Urine tests – to check protein levels. An abnormally high level of protein in the urine is one of the first signs of diabetic nephropathy.
  • Blood pressure – regular checks for raised blood pressure are necessary. Elevated blood pressure is caused by diabetic nephropathy and also contributes to its progression.
  • Blood tests – to check the degree of kidney function.
  • Biopsy – a small tag of tissue is removed from the kidney, via a slender needle, and examined in a laboratory. This is usually only performed when there is doubt about whether kidney damage is due to diabetes or to another cause.
  • Kidney ultrasound – enables the size of the kidneys to be imaged and allows the arteries to the kidneys to be checked for narrowing that can cause decreased kidney function.

Treatment options

There is no cure for diabetic nephropathy. Treatment must become ever more aggressive as the kidneys deteriorate towards failure. Medical options include:
Prevention – this is the best form of treatment and includes good control of blood glucose levels and blood pressure.
Medications – including medications to reduce high blood pressure, particularly angiotensin converting enzyme (ACE) inhibitors and angiotensin receptor blockers to curb kidney damage.
Dialysis – or artificial kidney treatment. End stage kidney failure is the failure of the kidney to function at all. Dialysis involves either shunting the patient’s blood through a special machine (haemodialysis) that helps remove the wastes while preserving water and salts, or removing wastes through fluid introduced into the abdomen (peritoneal dialysis). Dialysis is required several times every week for the rest of the person’s life.
Kidney transplant – a healthy donor kidney, obtained either from someone who has died or from a relative or friend, replaces the function of the diseased kidneys.

Risk reduction strategies

A person with diabetes can reduce their risk of diabetic nephropathy, or at least delay its onset, in a number of ways including:

  • Strictly controlling blood sugar levels
  • Making sure that blood pressure is well controlled
  • Avoiding non-steroidal anti-inflammatory drugs (NSAIDS)
  • Treating urinary tract infections promptly with antibiotics
  • Drinking plenty of non-alcoholic fluids, preferably water
  • Avoiding medical treatments that stress the kidneys, such as x-rays requiring the injection of contrast dyes
  • Having regular tests to ensure the health of your kidneys.

Things to remember

One of the causes 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.

There is no cure, and treatment must become ever more aggressive as the kidneys deteriorate towards failure.

Treatment options include medications, dialysis and kidney transplant.

Source & More Info: Patient.co.uk and Better Health Channel

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