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EMBARGOED FOR RELEASE
Wednesday, May 18, 2005
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CONTACT:
NHLBI Communications Office
(301) 496-4236
E-mail:
nhlbi_news@nhlbi.nih.gov |
New Kidney Function Test Better than Standard at Predicting
Death and Cardiovascular Outcomes
Cystatin-C, a new blood test for kidney function,
is a better predictor of death and cardiovascular risk
among the elderly than the standard measure of kidney
function, according to a National Heart, Lung, and Blood
Institute (NHLBI)-funded study published in the May 19
issue of the New England Journal of Medicine.
This more sensitive test distinguishes those at low, medium
and high cardiovascular risk, which may enable earlier
detection.
Investigators for NHLBI’s Cardiovascular Health
Study compared the two measures of kidney function,
cystatin-C and the standard test creatinine, as predictors
of death from all causes, death from cardiovascular
causes, and incidence of heart attack and stroke among
4,637 elderly participants in the study.
The 20 percent of the participants with the highest
levels of cystatin-C had twice the risk of death from
all causes as well as death from cardiovascular disease,
and a 50 percent higher risk of heart attack and stroke
compared with those who had the lowest levels of cystatin-C.
In contrast, testing the same participants with creatinine
detected a smaller high-risk group—about 10
percent of the participants—and all others appeared
to be at average risk.
With cystatin-C, investigators found that 60 percent
had abnormal kidney function putting them at medium
or high risk for cardiovascular complications.
It is estimated that 20 million Americans have significantly
reduced kidney function, and that even a small loss
of kidney function can double a person’s risk
of developing cardiovascular disease.
"This study affirms the important link between
kidney function and cardiovascular health and survival
in the elderly. If these findings are confirmed in
other studies, cystatin-C could be a useful prognostic
tool for evaluating older people at risk for not only
kidney disease, but cardiovascular disease as well,”
said Elizabeth G. Nabel, M.D., NHLBI director.
The standard evaluation of kidney function is an estimate
of the kidney’s rate of filtration—called
the glomerular filtration rate (GFR)— based
on measurement of creatinine in the blood and a further
calculation based on a patient’s age, gender
and race. Measurement of cystatin-C in the blood also
appears to reflect the GFR, but does not require an
additional calculation. Both creatinine and cystatin-C
are proteins found in the blood and filtered through
the kidneys. When the kidneys are not working well,
these proteins accumulate in the blood, which provides
a signal to the doctor that a person may have kidney
disease. Because creatinine is a by-product of muscle
cells. Its levels in the blood can be affected by
factors other than kidney disease, like age, gender,
race, and lean muscle mass. Cystatin-C is produced
by blood cells, and its levels in the blood are not
impacted by age, gender, race, or lean muscle mass.
Cystatin-C is FDA-approved for diagnostic use, but
the test is not yet widely available or commonly used
in clinical settings. This and other studies have
shown that cystatin-C may detect moderate kidney disease
at earlier stages, before creatinine levels would
rise, enabling identification of a much larger group
of people at risk for death and cardiovascular complications.
“Our results show that a normal creatinine is
not nearly as reassuring as we used to believe. In
persons at a high risk for kidney disease, such as
an older person or one with diabetes, hypertension,
or cardiovascular disease, a normal creatinine level
may be misleading us into thinking that the patient
is safe from the cardiovascular effects of kidney
disease,” said the study’s lead author
Michael Shlipak, M.D. M.P.H, of University of California
at San Francisco.
Dr. Shlipak noted that additional research is needed
to determine the exact clinical role for this test,
but that it may be most useful in high-risk patients
with normal creatinine. Evaluating the mechanisms
that underlie this strong association between the
kidney and cardiovascular disease would be critical
for targeting prevention efforts, he said.
Participants in the Cardiovascular Health Study were
aged 65 or older at baseline. Their creatinine and
cystatin-C measures were taken in 1992 or 1993 and
the average follow-up period was 7.4 years. The study
sites were Forsyth County, North Carolina, Sacramento
County, California, Washington County, Maryland and
the city of Pittsburgh.
Study co-authors are supported by grants from the
National Institute of Diabetes and Digestive and Kidney
Diseases.
To interview an NHLBI expert, please contact the NHLBI
Communications Office at (301) 496-4236. To interview
Dr. Shlipak, please contact the University of California,
San Francisco Department of Public Affairs at (415)
476-2557.
NHLBI is part of the National Institutes of Health
(NIH), the Federal Government's primary agency for biomedical
and behavioral research. NIH is a component of the U.S.
Department of Health and Human Services. Additional information
about cardiovascular disease and other NHLBI-supported
research and educational programs are available online
at the NHLBI Website, www.nhlbi.nih.gov.
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