Chronic kidney disease and functional limitation in older people: health, aging and body composition study

To assess whether chronic kidney disease (CKD) is independently associated with incident physical-function limitation.

Prospective cohort study.

Two sites: Pittsburgh, Pennsylvania, and Memphis, Tennessee.

Two thousand one hundred thirty-five men and women aged 70 to 79 without functional limitation at baseline from the Health, Aging and Body Composition Study.

Functional limitation was defined as difficulty in walking one-quarter of a mile or climbing 10 steps on two consecutive reports 6 months apart (in the same function). Kidney function was measured using serum cystatin C. Estimated glomerular filtration rate (eGFR), using the Modification of Diet in Renal Disease formula (<60 versus > or =60 mL/min per 1.73 m(2)), was a secondary predictor. Muscle strength, lean body mass according to dual energy x-ray absorptiometry, comorbidity, medication use, and inflammatory markers were evaluated as covariates.

Persons in the highest (> or =1.13 mg/L) quartile of cystatin C experienced a significantly higher risk of developing functional limitation than those in the lowest (<0.86 mg/L) quartile (hazard ratio (HR)=1.70, 95% confidence interval (CI)=1.40-2.07). The association between the fourth cystatin C quartile and functional limitation remained after adjustment for demographics, lean body mass, comorbidity, muscle strength, and gait speed (HR=1.41, 95% CI=1.13-1.75), although the association was attenuated after adjustment for markers of inflammation (HR=1.15, 95% CI=0.90-1.46). Similar results were found for eGFR less than 60 mL/min per 1.73 m(2), although the association with functional limitation remained after adjustment for inflammatory markers (HR=1.30, 95% CI=1.08-1.56).

CKD is associated with the development of functional impairment independent of comorbidity, body composition, and tests of strength and physical performance. The mechanism may be related to a heightened inflammatory state in CKD.