Health Views: James J. Onorato, M.D., Ph.D.
Diabetes and Kidney Disease
By James J. Onorato, M.D., Ph.D.
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James J. Onorato, M.D.,
Ph.D., a graduate of Case Western Reserve
University in Ohio, completed his training
in Internal Medicine and Nephrology at Duke
University. He is board certified in both
specialties. |
As the number of people affected with diabetes
has grown each year, so has the number of patients
who will require replacement of their kidney
function by dialysis or kidney transplantation. When
a patient’s kidney function is less than 10 percent,
they have reached End Stage Renal Disease (ESRD) and
dialysis is required to continue to live. The time
to act to preserve your kidney function is long
before this point. It is important to test your
kidney function early and review current steps to
slow the damage caused by diabetes with the hope of
avoiding ESRD.
Diabetes and the Kidney The earliest sign of
kidney damage by diabetes (referred to as
nephropathy) is the leak of albumin (a major blood
protein) thru the filtering part of the kidney and
into the urine. The filtering part of the kidney is
known as the glomerulus. This structure looks like a
tiny colander and serves to filter the blood of
waste products while retaining proteins and blood
cells which your body needs. A simple test is
available to look for low levels of albumin in the
urine (referred to as microalbuminuria). Since
fever, urinary tract infections, dehydration and
other renal problems can cause an elevation in the
microalbuminuria measurement, this test should be
confirmed by a total of three separate urine tests
over the course of six months. Untreated,
persistently high levels of albumin loss thru the
kidney are associated with a 40 percent chance of
developing ESRD in the Type II diabetic and up to 80
percent in the Type I patient. After two to five
years of microalbuminuria, the albumin leak becomes
so great that it is easily detected on the common
dipstick urine test as part of a routine urinalysis.
This is now referred to a proteinuria. Over the next
few years, the kidneys begin to decline in their
ability to filter the blood of waste products. Much
like a sink with a partially clogged drain, these
waste products slowly accumulate in the blood stream
and represent the next phase of kidney disease
referred to as renal insufficiency. Your doctor can
perform a simple blood test known as the serum
creatinine test to measure these accumulating waste
products. Once the creatinine level (which is
normally 1.2 mg/dl or less) has reached 1.5 to 2
mg/dl, more than 50 percent of the kidney function
has been lost and Chronic Kidney Disease (CKD) is
present, while ESRD occurs when the kidney function
is ten percent or less (serum creatinine of five to
tenmg/dl depending upon age, muscle mass and
gender).
Treatment Options Treatments are available to
slow and perhaps prevent the development of diabetic
renal disease. They require early detection as the
sooner treatment is started, the less damage will
occur within the kidney.
Patients with Type II diabetes should be screened
for microalbuminuria as soon as they are diagnosed
with diabetes. Since a number of years may have
passed in which the patient with Type II diabetes
may have had the disease but not been diagnosed, a
patient may already have diabetic kidney disease.
Type I diabetics are usually diagnosed very early in
their disease and do not develop albumin leakage for
5 to 10 years after the initial diagnosis. As
discussed above, a total of three separate urines
should be tested in a three to six month interval to
confirm the finding of microalbuminuria.
Studies have now shown that you can dramatically
reduce the chances of developing diabetic kidney
disease with intensive blood sugar control. The goal
of every diabetic patient and their physician needs
to be directed at lowering the glycosylated
hemoglobin (HgB A1c) level to less than seven
percent. Patients with HgB A1c levels of seven
percent or lower have a less than 10 percent risk of
developing kidney disease. The higher the HgB A1c
level, the greater the chances that kidney damage
will occur.
Beyond good diabetic control, the next step in
slowing kidney damage by diabetes involves blood
pressure control. It is clear that reducing the
blood pressure to less than 130/80 mmHg not only
slows the progression of kidney disease, but it will
reduce the risk of heart attack and stroke. In the
case of diabetes, not all blood pressure medicines
are equal. It has been shown that Angiotensin
Converting Enzyme Inhibitors (ACEi) and Angiotensin
Receptor Blockers (ARBs) reduce proteinuria and slow
the loss of kidney function. These medications
should be used at the earliest detection of
microalbuminuria or hypertension in the diabetic
patient. Even if microalbuminuria is present without
high blood pressure, these medications should be
given to the patient. There are problems with these
medications which your physician should monitor.
First, these medicines should be avoided in pregnant
women. Second, a dry cough may develop with the ACEi
(about one in 20 patients). In patients with reduced
renal function, an increase in your potassium may
occur requiring a reduction in dietary potassium
intake, the addition of diuretics to cause urinary
loss of potassium, or stopping the medication
altogether.
And what if you are one of those patients who
cannot take and ARB or ACEi? Second-line medications
in the form of Diltiazem and Verapamil are used in
the place of the first-line medicines. Your
physician will monitor your kidney function and
potassium with simple blood tests. It is generally
accepted that a 60 percent reduction in proteinuria
is associated with preservation of renal function.
Most kidney specialists would recommend an ACEi to
start. If the blood pressure goal is not achieved, a
diuretic is the next step. If the blood pressure or
albuminuria goal is not met, Diltiazem or verapamil
should be added. Rarely, an ARB (or ACEi if already
taking an ARB) is added. Failure of these
medications to reduce the blood pressure and albumin
leak often relates to excessive sodium intake so a
low sodium diet is an essential component to the
treatment plan.
Finally, the question of diet needs to be
addressed. Most diabetic patients should already be
following an ADA diet with carbohydrate and caloric
restriction. In addition, a low fat diet is often
prescribed due to high cholesterol problems
associated with diabetics. The theory is that
breakdown products from protein metabolism cause an
extra strain on the poorly functioning kidney.
Therefore, restricting protein intake will lessen
the work of the kidney and preserve renal function.
While this works in rat models of renal disease, it
is less clear in human beings. Most renal physicians
would recommend a modest reduction in dietary
protein intake as part of the overall treatment
plan.
Diabetes is the leading cause of kidney disease
in the United States and is growing at an alarming
rate. The earliest stage of diabetic kidney disease
occurs with leakage of small amounts of albumin thru
the kidney and into the urine. Years after the onset
of albumin loss, the damage to the kidney is so
extensive that the kidney no longer filters the
blood of waste products leading to renal failure and
ESRD. Treatments involving blood sugar control,
blood pressure control using ARB or ACEi, and
dietary protein restriction are critical in slowing
and perhaps preventing the progression of renal
disease in the diabetic patient. A team approach
including your primary care physician, diabetologist,
nephrologist, and dietician can be of great service
to the patient willing to commit to the lifestyle
changes needed to effectively deal with the
treatment of diabetic renal disease.
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