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Muscle mass may not fully explain higher
Creatinine in Blacks with Kidney Disease
Newswise — Why do black
patients with advanced kidney disease have
higher levels of creatinine, a standard
indicator of kidney function, than whites?
Contrary to what
doctors have thought, the difference may not
necessarily reflect differences in muscle
mass related to younger age or differences
in body composition, reports a study in the
July 2008 issue of the Clinical Journal
of the American Society of Nephrology (CJASN).
Led by Dr Joy Hsu of
University of California, San Francisco,
School of Medicine, the researchers measured
serum creatinine concentrations and
estimated body composition in more than
3,000 dialysis patients.
Doctors measure
creatinine to estimate how well a patient's
kidneys are functioning—a higher creatinine
level is generally a sign of lower kidney
function. Creatinine levels were compared
for black patients versus those of other
racial/ethnic groups.
As in previous studies,
blacks had higher creatinine levels than
non-black patients.
"A widely assumed
explanation for this racial difference is
that black patients tend to develop
end-stage kidney disease earlier than
whites," Dr Hsu explains.
"So blacks on dialysis
tend to be younger than whites and persons
of other races and ethnicities and so may
have more muscle mass, and creatinine is a
natural breakdown product of muscle."
To test this
assumption, the researchers used a technique
called bioelectrical impedance analysis to
estimate the patients' muscle mass.
"We hypothesized that
adjusting for muscle mass and related
factors would eliminate or reduce the racial
differences in serum creatinine level," says
Dr Hsu.
However, even after
adjustment, creatinine levels continued to
be significantly higher for black patients.
"The higher
creatinine levels in black patients compared
to non-black patients could not be entirely
explained by differences in age, sex, body
size, or muscle mass," according to Dr Hsu.
In the United States,
rates of kidney disease—including end-stage
renal disease (ESRD), requiring dialysis or
transplantation to replace lost kidney
function—are substantially higher among
blacks than whites.
The higher serum
creatinine levels in black patients are
another significant difference. "It is also
unclear how this racial difference in
creatinine levels is related to racial
differences in kidney disease," says Dr.
Hsu.
If muscle mass isn't
necessarily the answer, more research will
be needed to find the real reason why black
patients have higher blood creatinine levels
than white patients, Dr. Hsu adds.
"Perhaps the answer or
answers to this question will help explain
why blacks are affected by progressive
chronic kidney disease more so than whites."
The study, entitled
"Higher Serum Creatinine Concentrations in
Blacks with Chronic Kidney Disease: Beyond
Nutritional Status and Body Composition,"
will be available online at http://cjasn.asnjournals.org/
beginning Wednesday, April 16, 2008 and in
print in the July 2008 issue of CJASN.
The American Society of
Nephrology (ASN) is a not-for-profit
organization of 11,000 physicians and
scientists dedicated to the study of
nephrology and committed to providing a
forum for the promulgation of information
regarding the latest research and clinical
findings on kidney diseases. ASN publishes
the Journal of the American Society of
Nephrology (JASN), the Clinical
Journal of the American Society of
Nephrology (CJASN), and the
Nephrology Self-Assessment Program (NephSAP).
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