December 29, 2010
Simple Blood Test Indicates People at High Risk for Kidney Disease
(Ivanhoe Newswire) "“ A simple blood test can effectively indentify people at increased risk of developing complications associated with chronic kidney disease (CKD) at an earlier stage, according to this study.
To assess kidney function, doctors most often measure an individual's level of creatinine in the blood. Creatinine is produced by muscles and filtered by the kidneys. Unfortunately, creatinine tests are inaccurate at detecting mild kidney impairment, and creatinine levels can vary with muscle mass and protein intake. Recently, cystatin C blood measurements have emerged as an alternative test of kidney function. Because the protein is removed from the bloodstream by filtration in the kidneys, cystatin C levels rise in the blood when kidney function declines.
Carmen A. Peralta, MD, MAS, Michael G. Shlipak, MD, MPH (San Francisco Veteran's Affairs Medical Center and University of California, San Francisco) and their colleagues studied the ability of cystatin C levels to identify impaired kidney function. Their study included 11,909 participants from the Multi-Ethnic Study of Atherosclerosis (MESA) and the Cardiovascular Health Study (CHS), two studies designed to investigate various aspects of cardiovascular disease. The investigators defined CKD using both creatinine and cystatin C and compared their links to higher risks for premature death, cardiovascular events, heart failure, and kidney failure"”all of which are known complications of CKD.
In MESA, 9% of individuals had CKD by a creatinine-based equation only, 2% had CKD by a cystatin C-based equation only, and 4% had CKD by both equations. In CHS, these percentages were 12%, 4%, and 13%, respectively. Compared with those without CKD, individuals in MESA with CKD based on creatinine only had similar risk of premature death, while individuals with CKD based on cystatin C only had more than a 3-fold increased risk, and those with CKD based on both had nearly a 2-fold increased risk.
In CHS, individuals with CKD based on creatinine only also had a similar risk of premature death compared with those without CKD, while individuals with CKD based on cystatin C only had a 1.78-fold increased risk, and those with CKD based on both had a 1.74-fold increased risk. The pattern was similar for cardiovascular disease, heart failure, and kidney failure.
"Our findings suggest that the creatinine-based CKD definition captures a large number of adults who are actually at low risk for important complications of CKD. Based on our findings, we believe that cystatin C should be a confirmatory test among persons identified as having impaired kidney function based on creatinine levels," said Dr. Peralta. She noted that in doing so, individuals at highest risk may benefit the most from aggressive treatment and specialty referral. In addition, many other persons whose CKD is not confirmed by cystatin C may be reassured that they have low risk for CKD complications. Future research should investigate the cost-effectiveness of using multiple markers to identify and risk-stratify CKD.
SOURCE: Journal of the American Society Nephrology, published online December 2010