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Kidney Disease Of Diabetes Fact Book
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| Each year in the United States, nearly 80,000
people are diagnosed with kidney failure, a serious condition in which the
kidneys fail to rid the body of wastes. Kidney failure is the final stage
of a slow deterioration of the kidneys, a process known as nephropathy.
Diabetes is the most common cause of kidney failure, accounting for
more than 40 percent of new cases. Even when drugs and diet are able to
control diabetes, the disease can lead to nephropathy and kidney failure.
Most people with diabetes do not develop nephropathy that is severe enough
to cause kidney failure. About 16 million people in the United States have
diabetes, and about 100,000 people have kidney failure as a result of
diabetes.
People with kidney failure undergo either dialysis, which substitutes
for some of the filtering functions of the kidneys, or transplantation to
receive a healthy donor kidney. Most U.S. citizens who develop kidney
failure are eligible for federally funded care. In 1997, the Federal
Government spent about $11.8 billion on care for patients with kidney
failure.
African Americans, American Indians, and Hispanic Americans develop
diabetes, nephropathy, and kidney failure at rates higher than average.
Scientists have not been able to explain these higher rates. Nor can they
explain fully the interplay of factors leading to diabetic
nephropathy--factors including heredity, diet, and other medical
conditions, such as high blood pressure. They have found that high blood
pressure and high levels of blood glucose increase the risk that a person
with diabetes will progress to kidney failure.
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Two Types of Diabetes
There are two types of diabetes mellitus. In
patients with either type, the body does not properly process and use
certain foods. The human body normally converts carbohydrates to 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 pancreas. When a person does not make enough insulin, or the body does
not respond to the insulin that is present, the body cannot process
glucose, and it builds up in the bloodstream. High levels of glucose in
the blood or urine lead to a diagnosis of diabetes. Both types of diabetes
can lead to kidney disease.
Type 1 Diabetes
Only about 1 in 20 people with diabetes has type 1 diabetes, which
tends to occur in young adults and children. Type 1 used to be known as
insulin-dependent diabetes mellitus (IDDM) or juvenile diabetes. In type 1
diabetes, the body produces little or no insulin. People with type 1
diabetes must receive daily insulin injections. Type 1 diabetes is more
likely to lead to kidney failure. About 40 percent of people with type 1
develop severe nephropathy and kidney failure by the age of 50. Some
develop kidney failure before the age of 30.
Type 2 Diabetes
About 95 percent of people with diabetes have type 2 diabetes, once
known as noninsulin-dependent diabetes mellitus (NIDDM) or adult-onset
diabetes. Many people with type 2 diabetes do not respond normally to
their own or to injected insulin--a condition called insulin resistance.
Type 2 diabetes occurs more often in people over the age of 40, and many
people with type 2 are overweight. Many also are not aware that they have
the disease. Some people with type 2 control their blood glucose with meal
planning and physical activity. Others must take pills that stimulate
production of insulin, reduce insulin resistance, decrease the liver's
output of glucose, or slow absorption of carbohydrate from the
gastrointestinal tract. Still others require injections of insulin.
Between 1993 and 1997, more than 100,000 people in the United States were
treated for kidney failure caused by type 2 diabetes.
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The Course of Kidney Disease
The deterioration that characterizes kidney
disease of diabetes takes place in and around the glomeruli, the
blood-filtering units of the kidneys. Early in the disease, the filtering
efficiency diminishes, and important proteins in the blood are lost in the
urine. Medical professionals gauge the presence and extent of early kidney
disease by measuring protein in the urine. Later in the disease, the
kidneys lose their ability to remove waste products, such as creatinine
and urea, from the blood. Measuring these waste products in the blood
gives an indication of how far kidney disease has progressed.
Symptoms related to kidney failure usually occur only in late stages of
the disease, when kidney function has diminished to less than 10 to 25
percent of normal capacity. For many years before that point, kidney
disease of diabetes is a silent process.
Five Stages
Scientists have described five stages in the progression to kidney
failure in people with diabetes.
Stage I. The flow of blood through the kidneys, and therefore
through the glomeruli, increases--this is called hyperfiltration--and the
kidneys are larger than normal. Some people remain in stage I
indefinitely; others advance to stage II after many years.
Stage II. The rate of filtration remains elevated or at
near-normal levels, and the glomeruli begin to show damage. Small amounts
of a blood protein known as albumin leak into the urine--a condition known
as microalbuminuria. In its earliest stages, microalbuminuria may not be
detected on each evaluation. But as the rate of albumin loss increases
from 20 to 200 micrograms per minute, the finding of microalbuminuria
becomes more constant. (Normal losses of albumin are less than 5
micrograms per minute.) A special test is required to detect
microalbuminuria. People with type 1 and type 2 diabetes may remain in
stage II for many years, especially if they have good control of their
blood pressure and blood glucose levels.
Stage III. The loss of albumin and other proteins in the urine
exceeds 200 micrograms per minute. It now can be detected during routine
urine tests. Because such tests often involve dipping indicator strips
into the urine, they are referred to as "dipstick methods." Stage III
sometimes is referred to as "dipstick-positive proteinuria" (or "clinical
albuminuria" or "overt diabetic nephropathy"). Some patients develop high
blood pressure. The glomeruli suffer increased damage. The kidneys
progressively lose the ability to filter waste, and blood levels of
creatinine and urea-nitrogen rise. People with type 1 and type 2 diabetes
may remain at stage III for many years.
Stage IV. This is referred to as "advanced clinical
nephropathy." The glomerular filtration rate decreases to less than 75
milliliters per minute, large amounts of protein pass into the urine, and
high blood pressure almost always occurs. Levels of creatinine and
urea-nitrogen in the blood rise further.
Stage V. The final stage is kidney failure. The glomerular
filtration rate drops to less than 10 milliliters per minute. Symptoms of
kidney failure become apparent.
These stages describe the progression of kidney disease for most people
with type 1 diabetes who develop kidney failure. For people with type 1,
the average length of time required to progress from onset of kidney
disease to stage IV is 17 years. The average length of time to progress to
kidney failure is 23 years. Progression to kidney failure may occur more
rapidly (5-10 years) in people with untreated high blood pressure. If
proteinuria does not develop within 25 years, the risk of developing
advanced kidney disease begins to decrease. Type 1 diabetes accounts for
only 5 to 10 percent of all diagnosed cases of diabetes, but type 1
accounts for 30 percent of the cases of kidney failure caused by diabetes.
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Effects of High Blood Pressure
High blood pressure, or hypertension, is a major factor in the
development of kidney problems in people with diabetes. Both a family
history of hypertension and the presence of hypertension appear to
increase chances of developing kidney disease. Hypertension also
accelerates the progress of kidney disease where it already exists.
In the past, hypertension was defined as blood pressure exceeding 140
millimeters of mercury-systolic and 90 millimeters of mercury-diastolic.
Professionals shorten the name of this limit to 140/90 or "140 over 90."
The terms systolic and diastolic refer to pressure in the arteries during
contraction of the heart (systolic) and between heartbeats (diastolic).
In 1997, the National Heart, Lung, and Blood Institute issued new blood
pressure goals specifically for people with diabetes and people with renal
insufficiency in the Sixth Report of the Joint National Committee on
Prevention, Detection, Evaluation, and Treatment of High Blood Pressure
(JNC VI). In JNC VI, the committee recommends that people with
diabetes keep their blood pressure at 130/85 or lower and that people with
renal insufficiency (proteinuria greater than 1 gm/24 hrs) keep their
blood pressure at 125/75 or lower.
Hypertension can be seen not only as a cause of kidney disease, but
also as a result of damage created by the disease. As kidney disease
proceeds, physical changes in the kidneys lead to increased blood
pressure. Therefore, a dangerous spiral, involving rising blood pressure
and factors that raise blood pressure, occurs. Early detection and
treatment of even mild hypertension are essential for people with
diabetes.
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Preventing and Slowing Kidney Disease
Blood Pressure
Medicines
Scientists have made great progress in developing methods that slow the
onset and progression of kidney disease in people with diabetes. Drugs
used to lower blood pressure (antihypertensive drugs) can slow the
progression of kidney disease significantly. One kind of drug,
angiotensin-converting enzyme (ACE) inhibitors, has proven effective in
preventing progression to stages IV and V.
Diuretics, beta-blockers, adrenergic nervous system modulators, and
calcium channel blockers also may enhance blood pressure control in
patients with diabetes mellitus.
An example of an effective ACE inhibitor is captopril, which doctors
commonly prescribe for treating kidney disease of diabetes. The benefits
of captopril extend beyond its ability to lower blood pressure: it may
directly protect the kidney's glomeruli. ACE inhibitors have lowered
proteinuria and slowed deterioration even in diabetic patients who did not
have high blood pressure.
Any medicine that helps patients achieve a blood pressure target of
125/75 or lower provides benefits. Patients with even mild hypertension or
persistent microalbuminuria should consult a physician about the use of
antihypertensive medicines.
Low-Protein Diets
A diet containing reduced amounts of protein may benefit people with
kidney disease of diabetes. In people with diabetes, excessive consumption
of protein may be harmful. Experts recommend that most patients with stage
III or stage IV nephropathy consume limited amounts of protein.
Intensive Management of Blood Glucose
Antihypertensive drugs and low-protein diets can slow kidney disease
when significant nephropathy is present, as in stages III and IV. A third
treatment, known as intensive management of blood glucose or glycemic
control, has shown great promise for people with type 1 and type 2
diabetes, especially for those in early stages of nephropathy.
Intensive management is a treatment regimen that aims to keep blood
glucose levels close to normal. The regimen includes frequently testing
blood glucose, administering insulin frequently throughout the day on the
basis of food intake and exercise, following a diet and exercise plan, and
frequently consulting a health care team. Some people use an insulin pump
to supply insulin throughout the day.
A number of studies have pointed to the beneficial effects of intensive
management. Two such studies, funded by the National Institute of Diabetes
and Digestive and Kidney Diseases (NIDDK) of the National Institutes of
Health, are the Diabetes Control and Complications Trial (DCCT)
and a trial led by researchers at the University of Minnesota Medical
School.
A third study, conducted in the United Kingdom, is the U.K. Prospective
Diabetes Study (UKPDS).
The DCCT, conducted from 1983 to 1993, involved 1,441 participants who
had type 1 diabetes. Researchers found a 50 percent decrease in both
development and progression of early diabetic kidney disease (stages I and
II) in participants who followed an intensive regimen for controlling
blood glucose levels. The intensively managed patients had average blood
glucose levels of 150 milligrams per deciliter--about 80 milligrams per
deciliter lower than the levels observed in the conventionally managed
patients.
In the Minnesota Medical School trial, researchers examined kidney
tissues of people with long-standing diabetes who received healthy kidney
transplants. After 5 years, patients who followed an intensive regimen
developed significantly fewer lesions in their glomeruli than did patients
not following an intensive regimen. This result, along with findings of
the DCCT and studies performed in Scandinavia, suggests that any program
resulting in sustained lowering of blood glucose levels will be beneficial
to patients in the early stages of diabetic nephropathy.
The UKPDS--a 20-year trial conducted in England, Ireland, and
Scotland--tested the effects of intensive glucose and blood pressure
control in people with type 2 diabetes and found similar benefits for this
group.
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Dialysis and Transplantation
When people with diabetes experience kidney
failure, they must undergo either dialysis or a kidney transplant. As
recently as the 1970s, medical experts commonly excluded people with
diabetes from dialysis and transplantation, in part because the experts
felt damage caused by diabetes would offset benefits of the treatments.
Today, because of better control of diabetes and improved rates of
survival following treatment, doctors do not hesitate to offer dialysis
and kidney transplantation to people with diabetes.
Currently, the survival of kidneys transplanted into patients with
diabetes is about the same as survival of transplants in people without
diabetes. Dialysis for people with diabetes also works well in the short
run. Even so, people with diabetes who receive transplants or dialysis
experience higher morbidity and mortality because of coexisting
complications of the diabetes--such as damage to the heart, eyes, and
nerves.
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Good Care Makes a Difference
If you have diabetes:
- Have your doctor measure your hemoglobin A-1-c level at least
twice a year. The test provides a weighted average of your blood
glucose level for the previous 3 months. Aim to keep it at less
than 7 percent.
- Work with your doctor regarding insulin injections, medicines,
meal planning, exercise, and blood glucose monitoring.
- Have your blood pressure checked several times a year. If
blood pressure is high, follow your doctor's plan for keeping it
near normal levels. Aim to keep it at less than 130/85. If you
have proteinuria, aim to keep your blood pressure at less than
125/75.
- Ask your doctor whether you might benefit from receiving an
ACE inhibitor.
- Have your urine checked yearly for microalbumin and protein.
If there is protein in your urine, have your blood checked for
elevated amounts of waste products such as creatinine.
- Ask your doctor whether you should reduce the amount of
protein in your diet. Ask for a referral to see a registered
dietitian to help you with meal planning.
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Keeping on Top of Your Condition
Keeping in tune with your disease or condition not only makes treatment less intimidating but also increases its chance of success, and has been shown to lower a patients risk of complications. As well, as an informed patient, you are better able to discuss your condition and treatment options with your physician.
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