An introduction to diabetes and kidney disease

Diabetes is the most common cause of end stage renal failure (ESRF). Although most people with diabetes do not develop kidney damage that is severe enough to cause ESRF, diabetes is responsible for up to a third of all new kidney disease cases. The factors that lead to kidney disease in people with diabetes is not fully understood. It seems that heredity, diet, and other medical conditions, such as high blood pressure are important. High blood pressure and high levels of blood sugar certainly increase the risk that a person with diabetes will develop kidney failure.

What is diabetes?

In diabetes, also called diabetes mellitus or DM, the body is unable to use certain foods effectively, especially carbohydrates. The human body normally converts carbohydrates (complex sugars found in starchy foods) into glucose (the simple sugar that is the main source of energy for the body's cells). To enter cells, glucose needs the help of insulin, a hormone produced by the body in the pancreas. When a person does not produce enough insulin, or the body is unable to use the insulin that is present, the glucose is unable to enter the cells and it builds up in the bloodstream. Measuring the level of glucose in the bloodstream provides the diagnosis of diabetes. It is also the high levels of glucose in the bloodstream that causes the damage to the body.

There are two types of diabetes mellitus: Type I, or insulin dependent diabetes and Type II, non-insulin dependent diabetes.

Type I - insulin dependent diabetes

Type I diabetes, insulin dependent diabetes (IDDM), is the more severe of the disease but is much less common than Type II. Type I occurs more in children and young adults and is less common in adults. In IDDM, the pancreas produces little or no insulin. As a result, people with IDDM must receive daily insulin injections to replace their normal production.

Type II - non-insulin dependent diabetes Most people with diabetes have non-insulin dependent diabetes (NIDDM), or Type II diabetes. It occurs more often in people over the age of 40. In NIDDM the pancreas is still producing insulin, but may not be making enough or for some reason, the body is unable to use it properly. Type II diabetes is associated with being overweight. Therefore, it can be controlled by careful selection of foods and exercise leading to weight loss. However, some people require tablets to stimulate production of insulin by the pancreas within their body or slow down the absorption of sugars from the stomach and gut into the blood stream. Even so, severe cases can be treated with insulin, although they are not technically Type I diabetics. Unfortunately both types of diabetes can lead to kidney disease, although Type I is more likely to cause it than Type II.

How does diabetes cause kidney disease?

The damage to kidneys caused by diabetes is called diabetic nephropathy. The kidneys are affected in two ways:

1. Damage to the glomeruli of the kidneys The high levels of glucose in the bloodstream causes damage to the glomeruli, the microscopic blood filters of the kidneys. The damage reduces the efficiency with which the kidneys filter the blood. The damage can range from mild to severe. Symptoms can include fluid retention in the form of swelling of the limbs, loss of sleep, tiredness, poor appetite, upset stomach, vomiting, weakness, and difficulty concentrating.

2. Damage to the kidney that affects its role in controlling blood pressure The high levels of glucose in the blood affect the kidneys role in controlling blood pressure. Sensors in the kidney falsely detect lower blood pressure because of damage that blocks the tiny vessels carrying blood through the kidney. These sensors then trigger a chain of chemical actions in the body which leads to the body raising blood pressure unnecessarily. In turn, the high blood pressure interferes with the function of the kidney by causing more damage to the glomeruli. Unfortunately, the symptoms of kidney failure usually occur only in the late stages of the disease, when the kidneys have been reduced to working at less than a quarter of their normal level. This is because the kidneys work to make up for the failing capillaries and hide the problem. In order to reduce the chance of damage it is important to control diabetes, by maintaining healthy blood sugar levels, as carefully as possible. Good control may slow the progression of the disease so that, although affected, the kidneys can still work well enough without medical intervention. Mild damage might cause only swelling of the kidneys and the loss of tiny amounts of protein from the blood as the filters do not work quite as well as they should. Severe damage in advanced kidney disease related to diabetes will cause high blood pressure, increasing levels of waste products in the blood stream and possibly total kidney failure. Who is affected by kidney disease? It can take a long period of time to develop kidney failure from diabetes, as much as 20 or more years. Men with diabetes are more likely to get kidney disease than women. Control of blood sugar levels and the effective treatment of high blood pressure are important in maintaining kidney function. Kidney failure is not an inevitable result of diabetes.

How does high blood pressure affect the kidneys?

High blood pressure (hypertension), is a major factor in the development of kidney problems in people with diabetes. The glomeruli, the filters of the kidney, do not work effectively in the presence of high blood pressure as it damages and scars their delicate structure. Therefore, less excess water and fewer waste products are removed. These build up in the body causing the symptoms of kidney failure. A family history of high blood pressure and the presence of high blood pressure increases the chances of developing kidney disease. High blood pressure will make any kidney damage worse where it already exists. What is high blood pressure? Blood pressure is measured in millimetres of mercury. Normal blood pressure is about 120 millimetres of mercury systolic over 70 millimetres of mercury diastolic but varies according to the gender, height and weight of a person. The term ‘systolic’ refers to the pressure in the arteries when the heart contracts or beats and ‘diastolic’ refers to the pressure between heartbeats when it is refilling before the next beat. High blood pressure is usually taken as any reading with a systolic greater than 140 mm/hg and a diastolic greater than 90 mm/hg. This is usually stated as 140 over 90. As noted above, diabetes itself can lead to hypertension as a result of damage to the kidney caused by the disease. The combination of high blood pressure damaging the kidneys and damage to the kidneys causing high blood pressure creates a vicious cycle. Therefore, the early detection and treatment of even mild hypertension are essential for people with diabetes.

How can high blood pressure be treated?

There are a large number of drugs available now to treat high blood pressure. These drugs, commonly known as anti-hypertensives, can slow the progression of kidney disease significantly. If you have high blood pressure you may already be using one of these. There are two types commonly in use, ACE (angiotensin-converting enzyme) inhibitors e.g. captopril and calcium channel blockers e.g. nifedipine. ACE inhibitors also seem to play a role in protecting the glomeruli from damage. Your doctor will prescribe these or other medicines for you if you need them as part of blood pressure control.

What happens to people with diabetes with end stage renal failure?

When somebody with diabetes reaches end stage kidney failure they will require medical help to replace the function of the kidney. This is called renal replacement therapy and is provided in the form of dialysis or a kidney transplant. Having diabetes does not mean that you cannot have dialysis and/ or a kidney/pancreas transplant.

How successful is renal replacement therapy?

Patients with diabetes are transplanted as successfully as those without diabetes. Dialysis for people with diabetes is as successful in the short term as it is for patients without diabetes. However, because of the other complications of diabetes, damage to other organs such as the heart, the eyes and nerves, patients with diabetes who receive renal replacement therapy do experience higher rates of illness and death.

Can the pancreas be transplanted with the kidney?

For people who are insulin dependent diabetics where the pancreas no longer produces insulin there is sometimes the possibility of transplanting the pancreas with the kidney from the donor. The pancreas can be transplanted on its own. However, pancreases transplanted together with a kidney have a higher success rate than a pancreas transplanted alone. If the operation is successful, the patient will no longer have diabetes, will not need insulin or blood sugar monitoring and is unlikely to develop diabetes again, unless the transplant fails. However, damage to other organs, such as the eyes or nerves, will not be reversed by a pancreas transplant , but new injury is prevented.

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