Sandra Yin

May 15, 2012

May 15, 2012 (Washington, DC) — Decreased lower-extremity physical performance is associated with greater risk for death in patients with chronic kidney disease (CKD), according to a study presented here at the National Kidney Foundation (NKF) 2012 Spring Clinical Meetings.

Patients with mild to moderate CKD who walked at a speed of 0.8 m/s or slower had a 2.9-fold increased risk for all-cause mortality, compared with patients who walked faster than 0.8 m/s. The study was 1 of 4, out of a field of nearly 400, that won an Outstanding Research Poster award at the meeting.

"What we found in this study, interestingly, is a potent association between lower-extremity physical performance measures and death," Baback Roshanravan, MD, MSPH, senior nephrology fellow at the Kidney Research Institute, University of Washington, in Seattle, told Medscape Medical News.

What came as a surprise was that lower-extremity physical performance measures were more strongly associated with death than one measure of upper-extremity performance — hand grip strength. It is possible that CKD affects larger muscle groups, he noted, rather than more distal ones.

Much emphasis, he noted, is given to biomarkers in the field. But not many have focused on whole-person measures of multiorgan system burden related to CKD. The performance measures the researchers used, he said, were thought to measure not only recognized organ damage, but also unrecognized multiorgan system burden, which correlates with quality-of-life outcomes, incidence of disability, hospitalization, and death in geriatric literature.

The researchers took performance measures that have been used in geriatric studies of people 70 years and older and applied them to a younger CKD population to see how closely they related to all-cause mortality.

For the study, they examined the associations between upper- and lower-extremity performance measures and all-cause mortality in 309 stroke-free patients with CKD (estimated glomerular filtration rate [eGFR] below 90 mL/min per 1.73 m²) who were not on dialysis or in wheelchairs. They measured grip strength, usual gait speed, timed up and go (getting up out of a chair from a fully seated position, walking about 4 m around a cone, and coming back to sit in the chair), and how far someone could walk in 6 minutes. Follow-up involved checking vital status semiannually with phone calls to study participants or their emergency contact.

After adjustment for age, sex, race, body mass, diabetes, heart disease, and eGFR by cystatin c, each 0.1 m/s slowing in gait speed was associated with an estimated 34% greater risk for death (95% confidence interval [CI], 16% to 54%). Each second added to the timed up and go was linked to an estimated 11% greater risk for death (95% CI, 4% to 19%). A timed up and go speed of 12 s or more was associated with an estimated 2.48-fold greater risk for death (95% CI, 1.10 to 5.56). Dr. Roshanravan noted that the low number of deaths limited the precision of the estimates.

The study is significant, said Dr. Roshanravan, because not everyone who has a low GFR, signifying low renal function, is burdened by their illness. "It's important to characterize that burden for risk assessment later on, whether it's progression to death or other adverse outcomes," he explained.

Linda Fried, MD, MPH, staff physician at the VA Pittsburgh Healthcare System and professor of medicine and epidemiology at the University of Pittsburgh in Pennsylvania, was also a member of the NKF poster award committee, told Medscape Medical News that it might be possible to intervene at earlier stages to decrease adverse events for these patients. Because it is possible to improve physical function with exercise, a question arises, said Dr. Fried: If we had somebody here at higher risk, would exercise change that risk?

Dr. Roshanravan said that future work will include an intervention trial that looks at improvements in physical performance in CKD patients.

The Seattle Kidney Study was funded by an unrestricted grant from the Northwest Kidney Centers with continuing support from National Institute of Diabetes and Digestive and Kidney Diseases. Dr. Roshanravan reports receiving funding from a T32 training grant from the National Institutes of Health. Dr. Roshanravan and Dr. Fried have disclosed no relevant financial relationships.

National Kidney Foundation (NKF) 2012 Spring Clinical Meetings. Poster 112. Presented May 10, 2012.


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