April 19, 2010

Millions with ‘silent’ hypertension may have kidney disease

As many as 8 million adults in the United States who have undiagnosed or early-stage hypertension may also have kidney disease, putting them at higher risk for what may be preventable kidney failure, new research led by Johns Hopkins suggests.

The researchers found that 27.5 percent of those with diagnosed hypertension also had kidney disease, while 13.4 percent of those with normal blood pressure have kidney disease. In people with early-stage hypertension (or pre-hypertension), 17.3 percent had kidney disease; in those who had undiagnosed hypertension, 22 percent had kidney disease.

Meanwhile, experts estimate that nearly a third of Americans with high blood pressure have no knowledge of the disorder and are unaware that their blood pressure is in the danger zone. Consequently, they may not seek testing and treatment for hypertension or for kidney disease, an associated condition.

“There’s likely a very large group who have kidney disease and don’t know about it,” said Deidra C. Crews, the study’s leader and a nephrology instructor at the Johns Hopkins University School of Medicine. “If someone doesn’t know they have kidney disease, they’re likely not taking steps like altering diet, taking medication or making other lifestyle changes needed to avoid losing all kidney function.”

Published online in the journal Hypertension, the study for the first time estimates the prevalence of kidney disease among people with varying degrees of hypertension. Crews and her colleagues on the Centers for Disease Control and Prevention’s Chronic Kidney Disease Surveillance Team examined data from the National Health and Nutrition Examination Survey from 1999 to 2006, looking at records from nearly 18,000 participants for whom information on blood pressure and kidney function was available.

Kidney disease rates were based on testing of creatinine levels in the blood and proteins in the urine, and were estimated using guidelines from the National Kidney Foundation. If left untreated, chronic kidney disease can lead to kidney failure, the need for dialysis or a transplant and even death.

An estimated 26 million adults in the United States have chronic kidney disease, and that number is growing. Part of the increase has been attributed to rising obesity rates, kidney specialists say. Obese people are at high risk for diabetes and hypertension, the two leading causes of end-stage renal disease. Also contributing to rising rates of kidney disease may be the salt found in many popular processed foods. Too much salt in the diet is a risk factor for hypertension.

Crews said that she hopes her findings will resonate with both physicians and patients. “For people who have pre-hypertension, an alarm should go off in their physicians that says maybe this person should be tested for kidney disease,” she said. “And patients should know that having even pre-hypertension is a big risk factor for kidney disease, and they may need to make lifestyle changes.”

There is some debate in the medical community, Crews said, over what levels of kidney function and urine protein should be used to diagnose kidney disease. Her study uses current guidelines from the National Kidney Foundation. Some nephrologists say that those guidelines may be too loose and that stricter guidelines would paint a truer—if smaller—picture of the number of people who suffer from potentially life-threatening kidney disease.

Edgar R. Miller III, associate professor of medicine and epidemiology at the Johns Hopkins School of Medicine, was also part of the team that authored this study.

Related Web site

Chronic kidney disease research at Johns Hopkins