Researchers find that even modest kidney disease, even without noticeable symptoms, translates to a proportionately higher risk of heart disease independent of other risk factors such as smoking and obesity.
"My advice is that if you have family history of kidney disease, high blood pressure, or diabetes, get your kidney function tested -- especially if you are African American, and even if you don't yourself have these conditions," says study researcher Alan S. Go, MD, research scientist and senior physician at Kaiser Permanente in Oakland, Calif.
"You should be concerned if your GFR [glomerular filtration rate -- a measure of kidney function] is lower than 60 mL per minute. Make sure you're taking all necessary measures for cardiovascular health," he tells WebMD. "You should be even more concerned if it's below 45 mL per minute."
Because the kidneys filter blood and produce urine, a lower filtration rate means poorer kidney function.
Know Your Number
In a study published in this week's New England Journal of Medicine, Go notes that the risk of having a heart attack or dying of one increases even with modest abnormalities in kidney function.
Glomerular filtration rate is the best test to measure your level of kidney function and determine your stage of kidney disease. Your doctor can calculate your level.
Kidney failure has been associated with a higher risk of heart disease, but this study shows that even more modest degrees of kidney damage can increase that risk.
Compared with mild degrees of kidney damage, researchers found that moderate degrees of kidney damage -- GFR less than 60 mL/minute -- were associated with a significant increase in the risk of heart disease. More substantial decreases in kidney function (GFR less than 45 mL/minute) increased the risk of heart disease even more.
His study tracked more than 1.1 million middle-aged people for four years.
"It's important to know your [GFR] number, especially if you already have high blood pressure or diabetes," he says.
"Caught early, kidney disease can be managed through diet and medication, and these risks can hopefully be lowered."
What's the connection between even modest kidney damage and heart disease?
"I wish we knew conclusively," says Go. "What we do know is that people with reduced kidney function are more likely to go on to have heart disease."
In some people, kidney failure results from diseases such as diabetes and high blood pressure, both of which also increase the risk of heart disease. But several studies are under way, says Go, exploring other possible causes.
Kidney dysfunction may lead to more inflammation in heart blood vessels, which may in turn increase the risk of clogged arteries and heart disease, he says.
For now, Thomas H. Hostetter, MD, director of the National Kidney Disease Education Program, says Go's study suggests the "effectiveness of a simple, practical, but extremely important approach to assessing kidney function" -- having GFR measured, particularly in patients with a family risk of kidney problems.
Much as an eye examination can be used to gauge the degree of high blood pressure disease even outside the eye, kidney function seems to provide an index of overall blood vessel health, he writes in an editorial accompanying Go's study.