Alternative Test Uncovers Hidden Risks for Kidney, Cardiovascular Disease

Patients with high cystatin C protein levels were 50% more likely to die, study says

MONDAY, Aug. 14, 2006 (HealthDay News) -- Elevated blood levels of the protein cystatin C accurately predict increased risk for chronic kidney disease, cardiovascular disease, and death among elderly people who have no known kidney trouble, says a U.S. study.

These risks are not detected by the standard kidney function test, which measures levels of the protein creatinine, the study said. Creatinine, an end-product of muscle metabolism that's filtered through the kidney, has been a standard marker of kidney health for about a century.

Cystatin C is a blood protein that's also filtered through the kidneys.

The researchers measured levels of cystatin C and creatinine in blood samples from 4,663 people, age 65 and older, and matched those results with health outcomes up to nine years later.

Among people with no diagnosed chronic kidney disease, those with high levels of cystatin C had a significantly greater risk for poor health than those with normal levels of cystatin C. People with high cystatin C levels were 50 percent more likely to die overall, almost twice as likely to die of cardiovascular problems, and 30 percent more likely to die of non-cardiovascular problems.

Those with high cystatin C levels were three times more likely to develop chronic kidney disease, 40 percent more likely to suffer heart failure, 30 percent more likely to have a heart attack, and 20 percent more likely to have a stroke.

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

"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," study lead author Dr. Michael Shlipak, chief of general internal medicine at the San Francisco VA Medical Center, said in a prepared statement.

"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. (The study) 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," said Shlipak, who is also an associate professor of medicine, epidemiology, and biostatistics at the University of California, San Francisco.

The study was published in the Aug. 15 issue of the journal Annals of Internal Medicine.

More information

The U.S. National Kidney Disease Education Program has more about kidney disease.

SOURCE: University of California, San Francisco, news release, Aug. 14, 2006
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