In a surprising finding, researchers at UC San Francisco have discovered that the prevalence among Americans of chronic kidney disease (CKD), a condition that costs Medicare tens of billions of dollars to treat each year, hasn't increased since the early 2000s. The authors say the new study offers a promising sign that medical interventions aimed at controlling diabetes and high blood pressure – the two greatest risk factors for developing CKD – are working.
“We're making a dent in the fight against CKD,” said principal investigator Neil Powe, MD, MPH, MBA, a professor of medicine at UCSF who also heads the Chronic Kidney Disease Surveillance System for the Centers for Disease Control and Prevention (CDC). The new research appears online in the Aug. 1 issue of Annals of Internal Medicine.
CKD affects the kidneys’ ability to filter wastes and excess fluids from the body. When left untreated, CKD can progress to kidney failure, or to end-stage renal disease (ESRD), an incurable disease that can only be managed through dialysis or a kidney transplant. CKD can also lead to cardiovascular disease and premature death.
More than 20 million Americans are affected by CKD, though those in earlier stages of the disease are often unaware they have it, and more than 20 percent of the Medicare budget is devoted to treating patients with CKD and ESRD. A number of previous studies reported increases of up to 5 percent in CKD prevalence per year but didn't incorporate the most recent available data.
In the new work, the researchers examined data from the National Health and Nutrition Examination Survey (NHANES) gathered from 1988 through 2012 on stage 3 and 4 CKD, which are characterized by moderate to severe kidney damage that precedes the final stage. They found the overall prevalence of the disease had plateaued at around 7 percent of the U.S. population since the 2003 to 2004 survey, an unexpected but "encouraging" finding, Powe said.
“When you're trying to decrease ESRD, the first thing you want to do is decrease the prevalence of earlier stages of the disease,” Powe explained. “This reversal of the trend of rising CKD rates should ultimately mean less end-stage renal failure. That's our hope.”
African-Americans were the only racial/ethnic group to see a continued increase in CKD prevalence, from 3.7 percent of stage 3-4 CKD in the period from 1988 to 1994 to 6.2 percent in 2011 and 2012, a finding that Powe said is “concerning.”
“This is the group with the highest risk of developing end-stage kidney disease, and needing to have dialysis or a transplant," he said. "African Americans have two to three times the risk of developing end-stage kidney failure than any other racial or ethnic group."
Due to this increased risk of developing the disease, Powe believes treatment of diabetes and high blood pressure should be intensified for African-American patients.
The number of cases of ESRD per million people in the U.S. decreased from 386 in 2003 to 351 in 2013, prompting the UCSF researchers’ curiosity about whether that decline was due to lower rates of kidney disease overall or if people with CKD weren't progressing to the final stage of the disease.
The researchers analyzed information from NHANES, a nationally representative survey from the National Center for Health Statistics that incorporates patient lab data, for the periods from 1988 to 1994 and for every two years from 1999 to 2012, focusing on those patients with stage 3-4 CKD. Patients' stages were determined by their estimated glomerular filtration rate (eGFR), a number derived from levels of creatinine, a muscular waste product healthy kidneys dispose of, as well as patient demographics such as sex and age.
Stages 3-4 CKD prevalence among all Americans increased from a 1988–1994 rate of 4.8 percent to a rate of 6.9 percent in 2003–2004, but the percentage remained roughly the same after 2004. Women had a slightly higher rate than men: it increased from 5.6 percent in 1988–1994, to 8.1 percent in 2003–2004, and to 7.8 percent in 2011–2012, compared to men's average of 4.1 percent, 5.7 percent, and 5.9 percent, respectively.
When the researchers expanded the definition of CKD to include people bordering the qualifying eGFR level, the results showed the same stability in prevalence. People over 65 had a higher prevalence of CKD, but all age groups' rates plateaued after the early 2000s.
“It is rather remarkable that, despite the aging of the U.S. population, and the fact that there are more people with obesity and diabetes, the prevalence of chronic kidney disease seems to have stabilized over the most recent decade," said Chi-yuan Hsu, MD, professor of medicine at UCSF and a senior author of the study. “To me, this strongly suggests that medical interventions we have developed to retard development and progression of CKD are effective. This shows the importance of getting all eligible patients into proper treatment for their conditions.”
In addition to Powe and Hsu, UCSF authors of the study include Charles McCulloch, PhD, professor of medicine; Feng Lin, principal statistician in the Department of Epidemiology and Biostatistics; and Tanushree Banerjee, PhD, research specialist in the School of Medicine. Other coauthors are Jennifer Bragg-Gresham, PhD; Hal Morgenstern, PhD; and Rajiv Saran, MD, of the University of Michigan; Daniel Murphy, MD, who was a UCSF medical student at the time of the study and is now at the University of Minnesota; and Mark Eberhardt, PhD, and Meda Pavkov, MD, PhD, from the CDC.
The study was funded by grants from the American Society of Nephrology Foundation for Kidney Research Student Scholar Grant Program, the CDC and the National Institutes of Health.