Protein Levels in Urine Help Predict Kidney Function
TUESDAY Feb. 2, 2010 -- High protein levels in urine can signal trouble for people who are at risk for kidney failure and associated problems, a new study suggests.
The researchers reporting the findings in the Feb. 3 issue of the Journal of the American Medical Association are recommending that a test for protein levels in urine (proteinuria) be incorporated into upcoming new guidelines.
"Right now, the guidelines say you should use a blood test called serum creatinine [which measures a waste product processed by the kidneys] to give you an estimate of how well the kidneys are working," said study author Dr. Brenda R. Hemmelgarn, an associate professor of medicine at the University of Calgary in Alberta, Canada. "We found that including another marker of kidney health -- the level of protein in the urine -- helps to better predict risk than that single measure."
"I think it's very likely to get adopted in the new guidelines," she added. And, in fact, she is probably right.
"This is probably one of the most important data sets that was presented at a recent conference of experts to look at issues of chronic kidney disease classification and prognosis," said Kerry Willis, senior vice president of scientific activities at the National Kidney Foundation, which formulates international guidelines. "We do think it is an extremely important observation, and have set about starting to revise our guidelines. This is not a randomized, prospective trial, but for an observational data set this is about as compelling as it gets."
Those new guidelines are scheduled to be ready for public review in the late summer or early fall of 2011.
"We've scheduled the meeting. We're very busy here and wouldn't be doing this if we didn't think it was really important for patients," Willis said.
Chronic kidney disease is currently staged by looking at glomerular filtration, or how well the kidneys are removing waste products from the body. Lower eGFR (estimated glomerular filtration) levels indicate a higher likelihood of problems down the line, including heart attack and death.
The Canadian researchers based their conclusions on both eGFR and proteinuria measurements taken from almost one million adults between 2002 and 2007 in Alberta.
Patients with lower eGFR levels and higher proteinuria levels had higher rates of kidney failure, heart attack and death compared with higher eGFR levels and normal proteinuria levels.
Even when eGFR levels remained the same but proteinuria levels increased, the researchers noted higher rates of death, heart attack and impending kidney failure.
And patients with high proteinuria but near-normal eGFR also had worse clinical outcomes than those with somewhat lower eGFR without proteinuria.
"The surprising thing is that all levels of kidney function [among] patients that had higher proteinuria did worse," said Dr. Martin Zand, medical director of the kidney and pancreas transplant programs at the University of Rochester Medical Center.
In addition to revised screening guidelines, the world is also likely to see more studies to ferret out interventions would be most likely to help patients with abnormal proteinuria levels, Zand said.
"We've known that, for example, in people with diabetes and heavy protein in the urine, that reducing the amount of protein in the urine slows the progression of kidney disease and has been shown by many studies to reduce the other associated mortality," he said. "In this study, they show that even smaller levels of protein in the urine in people with relatively normal kidney function had worse health outcomes. It suggests that we need to figure out if the same interventions will work in [this population] as well."
The National Kidney Foundation has more on chronic kidney disease.
Posted: February 2010