Slow Walking Speed Linked with Premature Death in Patients with Chronic Kidney Disease

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Because chronic kidney disease (CKD) leads to the retention of metabolic waste products and hormonal disturbances, patients often experience skeletal muscle loss and dysfunction. New research published in the Journal of the American Society of Nephrology looks into a potential link between CKD patients’ impaired mobility and reduced physical performance and their risk of dying prematurely.

“Physical performance tests are objective measures used in gerontology to assess frailty, risk of disability, and to measure global comorbid burden,” said first author Baback Roshanravan, MD, of the University of Washington. “Little is known about physical performance and its association with all-cause mortality in younger CKD patients not treated with renal replacement therapy who are free of stroke and disability in their activities of daily living.”

Trial results

Roshanravan and his colleagues followed 385 patients with CKD without a history of stroke or disability and with an average age of 61 years and an average estimated GFR of 41 mL/min per 1.73 m2. Through various tests, the researchers compared handgrip strength, usual walking speed, six-minute walking distance, and timed up and go (the time that a person takes to rise from a chair, walk 4 meters, turn around, walk back to the chair, and sit down). The researchers were hoping to characterize patients’ physical performance and evaluate the utility of physical performance assessment in a referred clinic-based population of patients with CKD.

“First, CKD is associated with poor physical performance compared to the healthy population,” Roshanravan said. “Second, objective physical performance testing is an important bedside clinical tool that adds to the value of regular laboratory assessment of kidney function in discriminating those at high risk of mortality even among those without a history of stroke or disability in their activities of daily living.”

During an average of three years of follow-up, the investigators found that measures of lower extremity performance were at least 30 percent lower than predicted. Each 0.1-meter-per-second slower walking speed was linked with a 26 percent higher risk for death, and each one-second longer timed up and go was linked with an 8 percent higher risk for death. These associations were also seen even after excluding the subgroup with baseline self-reported mobility disability.

Walking speed and timed up and go more strongly predicted three-year mortality than kidney function or common blood tests. Adding walking speed to common laboratory tests of kidney function significantly improved the prediction of three-year mortality.

“We discovered that even after accounting for renal function, diabetes, and coronary artery disease, worse lower extremity physical performance was associated with all-cause mortality, but unexpectedly, this association after adjusting for renal function and comorbid illness was not seen with handgrip strength,” Roshanravan said. “Our findings suggest that lower extremity physical performance testing in chronic kidney disease patients may help identify those individuals who are more burdened by their CKD.”

Other experts agree that the findings may have a significant clinical impact.

“This novel study demonstrates that physical performance measures can improve the health assessment of persons with advanced chronic kidney disease. The key advantages of these measures are that they are low cost, non-invasive, and highly informative,” said Michelle Odden, PhD, who was not involved with the study and is an assistant professor of epidemiology at Oregon State University. “Additionally, these physical performance measures may provide insight into the systemwide health effects of chronic kidney disease.”

Odden’s research focuses mostly on kidney disease, cardiovascular outcomes, and loss of physical function in older adults.

Additional studies needed

As with any observational study, caution must be taken in this case against ascribing a causal relationship between lower extremity physical performance. The study provides no insights on whether lower physical activity may be a consequence of or a cause of lower physical performance in individuals with CKD.

Roshanravan also noted that the follow-up time in the study may not have been sufficiently long enough to detect significant differences in survival between those with strong and weak grip strength.

While more research is needed, the study’s findings suggest that measuring lower extremity physical performance may capture a complex set of skeletal muscle and neurologic impairments that develop in CKD patients and substantially affect their survival. The authors encourage additional investigations that look into the biological mechanisms underlying decreased physical performance in patients with CKD and that evaluate whether interventions that improve physical performance in CKD translate to improvements in health and longevity.

Notes

[1] Study co-authors include Cassianne Robinson-Cohen, PhD, Kushang Patel, PhD, Ernest Ayers, Alyson Littman, PhD, Ian de Boer, MD, T. Alp Ikizler, MD, Jonathan Himmelfarb, MD, Leslie Katzel, MD, PhD, Bryan Kestenbaum, MD, and Stephen Seliger, MD.

[2] Disclosures: Dr. Baback Roshanravan was funded by a Ruth L. Kirschstein National Research Service Award (NRSA) and T32 grant from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). The authors reported no other financial disclosures.


May 2013 (Vol. 5, Number 5)