Kidney Function and Survival in Older Patients after Rehabilitation Stay

In older patients discharged from inpatient rehabilitation, estimated glomerular filtration rate (eGFR) category and Barthel score are independent risk factors for survival; however, advanced chronic kidney disease (CKD) does not preclude successful rehabilitation. That was among the findings of an analysis conduced recently by Edward M. Doyle and colleagues reported in the American Journal of Kidney Diseases [2015;66(50:768-774].

With advancing age, the prevalence of CKD increases and 31% to 45% of individuals >70 years of age have CKD stage 3, defined as eGFR of 45-049 mL/min/1.73 m2, or worse. In people >75 years of age, there is an association between decreased kidney function and increased all-cause and cardiovascular mortality.

According to the researchers, it is unclear whether decreased kidney function and impaired physical function are independent risk markers for mortality in older persons or whether low GFR reflects frailty or impaired physical function, both strong markers for mortality in that population. Poor physical function and decreased capacity for exercise are often found in patients with CKD and previous studies have found an association between frailty and rapid decline in physical function in CKD patients, suggesting the importance of incorporating measures of physical function into analyses of outcomes for older CKD patients.

The current cohort analysis was designed to examine the effect of CKD on mortality in very old patients, accounting for the effect of physical function. The researchers also sought to assess the effect of CKD stage on the ability of older patients to have success in rehabilitation after illness. Data utilized were from prospective, routinely collected, linked clinical data sets on participants discharged from a single inpatient geriatric rehabilitation center from January 1999 to December 2011.

The study predictors were eGFR category at admission as a predictor of improvement in the 20-point Barthel score (measure of activities of daily living) during rehabilitation, discharge eGFR category, and Barthel score as predictors of survival after discharge.

Survival following discharge was modeled using Cox regression analyses, unadjusted and adjusted for age, sex, morbidities, Barthel score, and eGFR category on discharge, and serum calcium, hemoglobin, and albumin levels. Modeling of the effect of eGFR category at admission on change in Barthel score during admission was conducted with analysis of covariance, adjusted for admission, Barthel score, and comorbid conditions.

The analysis included 3012 patients who had data for all covariates, including discharge Bethel score. Mean age was 84 years and mean follow-up was 8.3 years; 2394 (79.5%) patients died during the follow-up period.

Compared with patients with eGFR of 60 to 89 mL/min/1.73 m2, adjusted hazard ratios for death were 1.29 (95% confidence interval [CI], 1.13-1.40), 1.45 (95% CI, 1.29-1.63), and 1.68 (95% CI, 1.42-1.99) for eGFR categories of 45 to 59, 30 to 44, and <30 mL/min/1.73 m2, respectively.

Within each eGFR category, the relationship between Barthel score at discharge and survival was similar: hazard ratios were 0.95, 0.93, 0.95, and 0.90 per Barthel score point within eGFR categories of ≥90, 60-89, 45-59, 30-44, and <30 mL/min/1.73 m2 (P for interaction, .2). For each admission category, similar improvements in Barthel score between admission and discharge were seen.

Study limitations cited by the researchers included the single-center study design and the use of routinely collected clinical data, which are incomplete. As a result, some variables of potential interest were not collected (detailed measures of cognition, weight, blood pressure, walk tests, and grip strength) or were collected for only a small subgroup (bicarbonate and phosphate measures).

“In conclusion, decreased kidney function is an independent contributor to increased mortality risk in the older population, However, it is not a barrier to successful rehabilitation even in the very old,” the researchers said.


Takeaway Points

  1. It is unclear whether decreased kidney function and impaired physical function are independent risk markers for mortality in older persons or whether low GFR reflects frailty or impaired physical function, both strong markers for mortality in that population.
  2. The current cohort analysis was designed to examine the effect of CKD on mortality in very old patients, accounting for the effect of physical function. The researchers also sought to assess the effect of CKD stage on the ability of older patients to have success in rehabilitation after illness.
  3. Compared with patients with eGFR of 60 to 89 mL/min/1.73 m2, adjusted hazard ratios for death were 1.29 (95% confidence interval [CI], 1.13-1.40), 1.45 (95% CI, .29-1.63), and 1.68 (95% CI, 1.42-1.99) for eGFR categories of 45 to 59, 30 to 44, and <30 mL/min/1.73 m2, respectively.