Novel Blood Test Highly Accurate for Predicting Kidney Disease Complications
Researchers say an accurate and inexpensive blood test that can determine the chances of developing complications from kidney disease that surpasses the currently used creatinine level.
For patients with kidney disease that commonly develops from diabetes and high blood pressure, the blood test, known as cystatin C, could accurately and inexpensively reveal the chances of complications that include heart disease, heart failure and kidney failure.
The good news is there has been much debate about when to start dialysis for patients with kidney failure. Measuring cystatin C is a test that costs about $17. Both creatinine and cystatin C are filtered by the kidneys and when levels rise in the bloodstream it signals the kidneys aren't working like they should.
The novel test offers information that was previously unavailable. In the study, conducted on 11,909 participants, researchers found patients with high creatinine levels, but normal cystatin C levels, were no more at risk for complications of kidney disease than those with normal levels of creatinine that builds in the bloodstream when the filtration capability of the kidneys declines.
Conversely, researchers found a "small but important segment" of the study group had normal creatinine blood levels but high cystatin C levels, whose risk for complications would have been overlooked.
Lead author Carmen A. Peralta, MD, MAS, an SFVAMC researcher and an assistant professor of medicine in residence in the division of nephrology at University of California, San Francisco explains, "...creatinine is a byproduct made in muscles, so it is affected by what you eat and especially by how much muscle you have.
A bodybuilder with healthy kidneys might have an elevated creatinine level because of high muscle mass, whereas a frail elderly person might have normal or even low levels of creatinine, but in fact this person's kidneys are not working well – it's just that there's not much creatinine because there's not much muscle."
The findings are compiled from data extracted from two prospective studies: the Multi-Ethnic Study of Atherosclerosis and the Cardiovascular Health Study, funded by the National Heart, Lung, and Blood Institute.
Cystatin C is more accurate for predicting complications of kidney disease because it is made by cells throughout the body and not just muscle cells.
Michael G. Shlipak, MD, MPH, chief of general internal medicine at SFVAMC says, "It's vital that we have an accurate diagnostic test, because kidney disease does not show symptoms until it's too late, when your kidneys have almost failed completely."
Peralta notes, "Being missed by creatinine is an important limitation in our current method of diagnosing kidney disease." Being told you have kidney disease from false positive test results is also disastrous. There is fear and psychological stress, particularly in communities of color, where people have a lot of friends and family members who are on dialysis," she noted. "You can also be subjected to unnecessary and expensive tests and medications."
The findings that measuring cystatin C levels with an inexpensive blood test to accurately predict who is at risk for complications of kidney disease are timely, as nephrologists struggle to establish guidelines for treating patients, including at what point to begin dialysis.
JASN: doi: 10.1681/ASN.2010050483