Kidney Test Reveals Problems

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      http://www.sciencedaily.com/releases/2006/08/
      060816083220.htm

Alternative Kidney Test Reveals Hidden Health Risks


Elevated blood levels of the protein 
cystatin C accurately predict higher risk of chronic kidney disease, 
cardiovascular disease, and death among elderly people with no known 
kidney problems -- risks that the standard kidney function test, which 
measures the protein creatinine, misses entirely, according to a study led 
by a researcher at the San Francisco VA Medical Center.

"For the clinician who treats older people or others at risk for kidney 
disease, this is an important message: A normal creatinine level should 
not reassure you that your patient has normal kidney function," says lead 
author Michael Shlipak, MD, chief of general internal medicine at SFVAMC 
and an associate professor of medicine, epidemiology, and biostatistics at 
the University of California, San Francisco. "It shows that cystatin is a 
very promising new tool that complements creatinine in the ongoing effort 
to detect early kidney disease and prevent its complications."

The study appears in the August 15, 2006 issue of Annals of Internal 
Medicine.

Shlipak and his colleagues tested blood samples from 4,663 elders living 
independently in the community who participated in the Cardiovascular 
Health Study, a national longitudinal study of people aged 65 and older 
sponsored by the National Institutes of Health.

The researchers measured each participant's creatinine -- an end-product 
of muscle metabolism that is filtered through the kidneys and has been a 
standard marker of kidney health for "probably 100 years," according to 
Shlipak -- and cystatin C, a blood protein that is also filtered through 
the kidneys. They then matched test results with health outcomes up to 
nine years later.

Among participants with no diagnosed chronic kidney disease, those with 
high levels of cystatin C had significantly greater risk for poor health 
than those with normal cystatin C levels. Individuals in the high cystatin 
group were 50 percent more likely to die overall, nearly twice as likely 
to die of cardiovascular problems, and 30 percent more likely to die of 
non-cardiovascular problems. They had increased risks of 40 percent for 
heart failure, 30 percent for heart attack, and 20 percent for stroke. 
Finally, they were more than three times more likely to develop chronic 
kidney disease.

"In contrast," the researchers report, "creatinine concentrations had 
associations with each outcome that were much weaker, and significant only 
for the outcome of cardiovascular death."

Shlipak says, "This tells us that the creatinine test, while broadly 
useful as a measure of kidney health, is insensitive. If a creatinine 
level is high, that's probably an indication of kidney disease. But if 
it's low, you don't know. You would need to do a cystatin test if there's 
any other indication of kidney disease or if the patient is in a group 
that's at risk."

Groups at risk for chronic kidney disease include people over 65, people 
with diabetes, hypertension, or cardiovascular disease, and African 
Americans, American Indians, and Hispanic Americans.

"This is also telling us that kidney function declines much more with age 
than we realized before," adds Shlipak. He terms this syndrome 
"pre-clinical kidney disease," or pre-CKD.

"We have the tools to slow kidney disease," he notes, including blood 
pressure control, sugar control for diabetes, and specific medications 
known as ACE inhibitors. "It's well-established that end-stage kidney 
disease is rising at a rate of 10 to 20 percent per year. With a 
heightened awareness of pre-CKD, we can be more aggressive in taking steps 
to prevent it."

Accurate knowledge of kidney function is also a matter of patient safety, 
according to Shlipak: "Surgery, some other medical procedures, and certain 
medications all can have an adverse impact on kidney health."

The cystatin test itself is relatively inexpensive and already widely 
available, he says. "As demand for it increases, it should become even 
more commonly available."

The next steps for researchers, says Shlipak, should include longitudinal 
studies that determine whether a screening test for cystatin C can improve 
clinical care and health outcomes for large patient populations. "We also 
want to map out the physiologic consequences of early mild kidney 
dysfunction, now that we can measure it."

Co-authors of the study are Ronit Katz, PhD, of the University of 
Washington; Mark J. Sarnak, MD, of Tufts-New England Medical Center; Linda 
F. Fried, MD, MPH, of the VA Pittsburgh Healthcare System; Anne B. Newman, 
MD, MPH, of University of Pittsburgh; Catherine Stehman-Breen, MD, MS, of 
Amgen, Inc.; Stephen L. Seliger, MD, Brian Kestenbaum, MD, and Bruce 
Psaty, MD, PhD, of the University of Washington; Russell P. Tracy, PhD, of 
the University of Vermont College of Medicine; and David S. Siscovick, MD, 
MPH, of the University of Washington.

The study was supported by funds from the National Heart, Lung, and Blood 
Institute, the American Federation for Aging Research, and the National 
Institute on Aging that were administered by the Northern California 
Institute for Research and Education, as well as funds from the Robert 
Wood Johnson Foundation and the Department of Veterans Affairs.
Adapted from materials provided by University of California - San 
Francisco.

University of California - San Francisco (2006, August 17). Alternative 
Kidney Test Reveals Hidden Health Risks. ScienceDaily. Retrieved March 24, 
2009, from http://www.sciencedaily.com /releases/2006/08/060816083220.htm