Kidney failure is one of the most well known and feared complications of diabetes and is uppermost on the mind of many patients when they first know about their diabetes. Dr Peter Eng, Senior Consultant, Director, SGH Diabetes Centre, spills the beans on kidney disease and what can be done to prevent, detect and delay kidney failure.
 

How does diabetes affect the kidneys?

The kidney is like a filter. In healthy people, the kidney filters out waste materials and excess water from the bloodstream but retains important molecules such as proteins in the blood. In long-standing diabetes, particularly when diabetes control has been poor, the kidney can get damaged. The filtering units in the kidney become less effective in filtering out waste products and also start to leak out protein molecules into the urine.
 

How long does it take to get kidney failure?

Diabetes affects the kidneys in a slow but progressive fashion and totally without any symptoms till kidney failure is well advanced. The damage can be divided into 4 main stages.

In the first stage (0 to 5 years from onset of diabetes), the kidney actually has an increase in filtration function.

In the second stage (5 to 15 years from the onset of diabetes), the kidney starts to leak out small amounts of protein. The medical term for this small amount of protein in the urine is 'microalbuminuria'. This is the stage in which the kidney damage can still be reversible.

At the third stage of kidney disease (10 to 15 years after the onset of diabetes), the kidney starts to leak out larger amounts of protein. The medical term for this is "proteinuria". Once the stage of proteinuria is reached, there is continuous deterioration of kidney function till the final stage of end-stage kidney failure (15 to 30 years after the onset of diabetes). At this stage, the kidney has minimal function and patient will either need dialysis or a kidney transplant.
 

How many patients with diabetes will end up with kidney failure?

Not everyone with diabetes will end up with end-stage kidney failure. After 10 Years of diabetes, it is estimated that 25% of patients will have microalbuminuria. Not all of these patients will proceed to develop the later stages of kidney disease. After 30 years of diabetes, it is estimated that about 15% of patients have end-stage kidney failure.

In Singapore, as well as in many other parts of the world, diabetes is the leading cause of end-stage kidney failure. While better medicines and better control of diabetes should reduce the proportion of diabetic patients who develop end-stage kidney failure, the total number of diabetic patients who end up with end-stage kidney disease is on the rise. This is partly due to the increase in the number of patients with diabetes as well as the fact that, with better treatment of heart disease, diabetic patients now live longer and more eventually develop advanced kidney disease.
 

How come some patients get kidney disease while others do not?

The percentage of patients who develop either microalbuminuria, proteinuria or end-stage kidney failure depends greatly on a number of different factors. Some of these factors can be modified and if well controlled, may prevent or delay the development of kidney disease.

The most important factors are blood glucose control and blood pressure control. Part of the reason may be genetic. The risk is higher if other family members are affected with diabetic kidney disease The risk is also higher in certain racial groups.
 

How will I know if I have kidney disease?

There are no symptoms of kidney disease until very late. Hence all patients with diabetes need to be screened for kidney disease on a regular basis. This is generally done about once a year. Early kidney disease at the stage of microalbuminuria can be detected by sensitive urine tests that can detect small amounts of albumin in the urine.

There are several ways to test for microalbuminuria. The simplest is using a special urine test strip that can detect small amounts of albumin. Other methods include an on-the-spot sample of urine or a 24-hour collection of urine, both of which are sent to the lab. Once microalbuminuria is detected, it is usually confirmed with a repeated test.

At the later stages of kidney disease, when proteinuria is present, this can be picked up with a routine urine dipstick. The amount of protein passed out in a day can be measured in a 24-hour urine collection. Once a year. a blood creatinine level is also done. This is to check the filtering ability of the kidney and if there is a significant degree of kidney damage, the creatinine level will rise.
 

What can be done once kidney disease is found?

As mentioned earlier, kidney disease that is detected at the early stage of microalbuminuria can be stabilised or even reversed. Major studies in both type 1 and type 2 diabetic patients have demonstrated that good glucose control can reduce the development or progression of kidney disease by 30 to 60%. The target for good glucose control is a HbA1c level of less than 6.5 to 7%. Similarly, if blood pressure is well controlled, there is again a reduction of development of kidney disease by 30%. The target for good blood pressure control is less than 130/80 mm Hg.

There are now many studies that show the kidney protective effects of two types of blood pressure lowering medications. The first type is called angiotensin converting enzyme inhibitors (ACE-inhibitors). The second type is called angiotensin II receptor blockers. Both these types of medication have demonstrated effectiveness at retarding both early (microalbuminuria) stage and later (proteinuria) stage kidney disease.

 

Other measures that can be implemented to retard kidney damage include avoidance of a high protein diet, weight loss, reducing cholesterol and stopping smoking. These are not as important as control of glucose and blood pressure but may still play a significant role in retarding the progression of kidney disease.

At a very advanced stage of kidney disease, when patients are reaching end-stage kidney disease, not too much can be done to retard the progression. Hence, the importance of detecting kidney disease early can not be overemphasised.
 

Conclusion

It should be remembered that while a significant proportion of patients with diabetes will have some degree of kidney damage, the majority do not end up with end-stage kidney failure requiring dialysis or transplantation. There are accurate and relatively simple methods to detect early kidney disease. This is vital as there are effective measures that can be taken to either stabilise or retard the progression of kidney disease.

The most important of these measures is good glucose control and good blood pressure control. Two classes of blood pressure lowering medicines have shown additional kidney protective benefits and are now the mainstay in the management of diabetic kidney disease. If diabetic kidney disease is detected early, much can still be done to try to delay or avoid end-stage kidney failure.