Functional Dependence and Mortality in the International Dialysis Outcomes and Practice Patterns Study (DOPPS)

Abstract

Background: Patients receiving long-term dialysis have among the highest mortality and hospitalization rates. In the nonrenal literature, functional dependence is recognized as a contributor to subsequent disability, recurrent hospitalization, and increased mortality. A higher burden of functional dependence with progressive worsening of kidney function has been observed in several studies, suggesting that functional dependence may contribute to both morbidity and mortality in dialysis patients.

Study design: Prospective cohort study.

Setting & participants: 7,226 hemodialysis patients from 12 countries in the DOPPS (Dialysis Outcomes and Practice Patterns Study) phase 4 (2009-2011) with self-reported data for functional status.

Predictor: Patients' ability to perform 13 basic and instrumental activities of daily living was summarized to create an overall functional status score (range, 1.25 [most dependent] to 13 [functionally independent]).

Outcome: Cox regression was used to estimate the association between functional status and all-cause mortality, adjusting for several demographic and clinical risk factors for mortality. Median follow-up was 17.2 months.

Results: The proportion of patients who could perform each activity of daily living task without assistance ranged from 97% (eating) to 47% (doing housework). 36% of patients could perform all 13 tasks without assistance (functional status = 13), and 14% of patients had high functional dependence (functional status < 8). Functionally independent patients were younger and had many indicators of better health status, including higher quality of life. Compared with functionally independent patients, the adjusted HR for mortality was 2.37 (95% CI, 1.92-2.94) for patients with functional status < 8.

Limitations: Possible nonresponse bias and residual confounding.

Conclusions: We found a high burden of functional dependence across all age groups and across all DOPPS countries. When adjusting for several known mortality risk factors, including age, access type, cachexia, and multimorbidity, functional dependence was a strong consistent predictor of mortality.

Keywords: Chronic kidney disease (CKD); Dialysis Outcomes and Practice Patterns Study (DOPPS); activity of daily living (ADL); dialysis; end-stage renal disease (ESRD); functional dependence; functional status; hospitalization; independence; morbidity; mortality; physical activity; quality of life (QoL).

Figure 1A. Functional Status (FS) score by country

Percents were rounded to the nearest integer and thus may not sum to 100%.

Figure 1B. Functional Status (FS) score by age, gender, and diabetes status

Percents were rounded to the nearest integer and thus may not sum to 100%.

Figure 2. Mortality risk (per year) by age and functional status (FS)

Discrete survival model with binomial distribution, logit link function, and log(follow-up) offset. Model was adjusted for country and included age as a cubic term and an interaction between FS category and age. Predicted probabilities for age*FS combinations used to estimate mortality risk.