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Reviewed by Professor Ian W Campbell, consultant physician
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What is diabetic kidney disease?
Long-standing diabetes causes changes in small blood vessels
that can lead to damage of the kidneys. This damage can result in severe kidney
failure.
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Term watch
Nephropathy: the medical term for the type of
kidney disease that occurs in diabetes.
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Subtle damage to the kidneys can start within a year or so of
Type 1 diabetes, and can be present at diagnosis in Type 2, but it usually
takes 5 to 10 years to become a noticeable problem.
Who gets diabetic kidney disease?
There are wide differences in estimates of how many people with
diabetes will
progress to having diabetic kidney disease - from 6 to 27 per cent of people
with
Type 1 diabetes, to
25 to 50 per cent of
Type 2.
Poor glucose control and even modestly
high blood pressure
can increase your risk of making kidney disease worse.
In Type 2 diabetes, people from an Asian or Afro-Caribbean
origin are twice as likely to develop diabetic kidney disease.
What are the symptoms?
There are no symptoms when diabetic kidney disease first
develops. Later, the following signs of decreased kidney function
are:
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fatigue
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nausea and vomiting
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itchy skin
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a metal taste in the mouth
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heartburn
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swelling in the limbs and/or eyelids due to the build-up of
fluid in the tissues (oedema).
What problems does diabetic kidney disease cause?
The kidneys are essential organs:
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they filter and eliminate the waste products of metabolism
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they have a central role in controlling blood pressure and
fluid balance in the body
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they produce the key hormone, erythropoietin, that stimulates
the bone marrow to manufacture red blood cells.
Diabetic kidney disease is the most common cause of kidney
failure in the UK.
People with very poor kidney function require some form of
artificial kidney support (dialysis) or a kidney transplant.
The increasing numbers of people with Type 2 diabetes has meant
the demand for these facilities has been steadily climbing for several
years.
Because the kidneys have a central role in controlling blood
pressure, it's common for people with diabetic kidney disease to have raised
blood pressure.
High blood pressure accelerates the decline in kidney function
in nephropathy – in other words the two problems multiply each other’s effect.
By lowering blood pressure, the rate of progression of diabetic kidney disease
can be slowed down.
A target blood pressure of 130/80mmHg is recommended for
diabetic patients with kidney disease.
How is diabetic kidney disease diagnosed?
The kidney filtering system normally ensures proteins are kept
almost completely out of urine. In diabetic kidney disease, these filters
become leaky and start to let protein through.
If protein is found in your urine, diabetic kidney disease is
likely to be present.
A diagnosis is made by measuring the amount of the protein
albumin in the urine. The urine sample is usually taken from the first urine
passed in the morning.
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A value below 20 milligrams (mg) is normal.
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A value between 20 and 200mg is called microalbuminuria (the
beginning of kidney disease).
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A value above 200mg is called proteinuria (a more advanced
stage of diabetic kidney disease).
Another way to assess albumin loss in the urine is to calculate
the albumin:creatine ratio in a first-pass morning urine sample.
If this ratio is more than 2.5mg/mmol in men or 3.5mg/mmol in
women then it's regarded as significant and could require tratment with ACE
inhibitors or angiotensin II antagonists.
Microalbuminuria is not a harmless stage that can be ignored
until it develops into more advanced kidney disease. People with
microalbuminuria are two to four times more likely to develop coronary heart
disease.
Checking urine for albumin is an important part of diabetes
management that should be done at least annually. Test kits are now available
that allow quick checks to be done in the GP's surgery.
What are the risk factors?
There is an increased risk of diabetic kidney
disease:
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with poor blood sugar control, ie levels are too high for too
much of the time.
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if you smoke
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if you're male
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if there's some protein in your urine
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if you have high blood pressure
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the older your are
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the longer you've had diabetes
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if you have raised levels of cholesterol and fats
(triglycerides) in the blood
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if you already have diabetic eye disease (diabetic
retinopathy).
This list has some things in common with that for diabetic
retinopathy.
How is diabetic kidney disease treated?
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By normalising blood sugar levels with insulin or blood sugar lowering
medicines.
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If microalbuminuria is detected, ACE inhibitors such as
Lopace (pamipril)
or angiotensin II antagonists (eg
Aprovel
(irbesartan) ) are used.
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If you have high blood pressure, it needs to be well controlled
and
blood pressure
medication may be given. In diabetic patients with kidney disease a target blood pressure level is 130/80mmHg.
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If kidney function is significantly reduced, you'll need to
reduce the amount of protein in your diet.
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If you have
end-stage kidney
disease, you'll need dialysis and ultimately a kidney
transplant.
ACE inhibitor drugs
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Good advice
ACE inhibitors and angiotensin II receptor blockers can be
given to a wide range of people, but they aren't suitable for all.
If widespread hardening of the arteries has reduced blood
supply to the kidneys, these drugs can worsen kidney function.
To confirm the drugs aren't causing problems, blood checks
on kidney function should be done shortly after starting treatment.
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These drugs are used to lower high blood pressure, but they
can also reduce the loss of the protein albumin through the
kidneys.
They've been shown to reduce the likelihood of heart attack in
Type 2 diabetes by 25 per cent when given over several years.
When Type 1 patients with diabetic kidney disease took the
drugs over three years, there was a 50 per cent reduction in all events
including dialysis, kidney transplantation and death.
ACE inhibitors are well tolerated drugs that can be given to a
wide range of people. The most common side effect is a dry cough that can be
troublesome enough to make the drug intolerable.
Angiotensin II receptor blockers
These drugs work in a different way to ACE inhibitors, but are
also used to control blood pressure. Their main advantage is their low tendency
to cause side effects – in particular they do not cause coughing.
Like ACE inhibitors, angiotensin II receptor blockers have
also been shown to be beneficial in diabetic kidney disease. Sometimes both
drugs are combined for added benefit.
One study looked at people with Type 2 diabetes and
microalbuminuria over two years. It found the number who went on to develop
high levels of protein in urine (proteinuria) was reduced by two thirds,
regardless of their blood pressure level.
In the long term
If microalbuminuria is detected at an early stage, treatment can
begin and the risk of aggravating kidney disease is lowered.
Good care of diabetes and risk factors such as high blood
pressure means only a small number of people with diabetes experience the
gradual decrease of kidney function that ends with dialysis and possible kidney
transplant.
Dialysis
Dialysis is the general term for treatments that can help
failing kidney function or replace it altogether. It's a successful technique
that helps most people. There are two types of dialysis:
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Haemodialysis involves putting blood of
through a filtering machine and then returning it to the body. Haemodialysis
requires expensive machinery and is usually done in hospital. Each session
takes several hours, and several sessions are required each week.
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Continuous ambulatory peritoneal dialysis
(CAPD) is a simpler type of dialysis that can be carried out at home. A plastic
tube is placed in the abdomen and led out to the skin surface on the tummy. The
tube can be left in place for several weeks. Fluid is run into the abdomen,
left for a few hours and then run out again, cleaning toxins from the blood.
CAPD can be carried out repeatedly and may be the only type of dialysis
needed.
Kidney transplant
A kidney transplant is the only way for someone with severe
kidney failure to receive long-term treatment that doesn't depend on machines
or dialysis.
People with diabetes can receive a kidney transplant as
successfully as any other person.
In some centres a transplant of the pancreas is done at the
same time as the kidney transplant – removing the need for insulin or tablet
treatment for diabetes.
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References
Home P, Mant J, Turner C, et al. Management of Type 2 diabetes:
summary of updated NICE guidance. BMJ 2008; 336: 1306-8.
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Based on a text by Dr Jan Erik Henriksen, Dr Ole Hother Nielsen and Professor Henning Bech-Nielsen
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Last updated 16.09.2008
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