Multiple measurements of depression predict mortality in a longitudinal study of chronic hemodialysis outpatients

The medical risk factors associated with increased mortality in hemodialysis (HD) patients are well known, but the psychosocial factors that may affect outcome have not been clearly defined. One key psychosocial factor, depression, has been considered a predictor of mortality, but previous studies have provided equivocal results regarding the association. We sought to determine whether depressive affect is associated with mortality in a longitudinal study of end-stage renal disease (ESRD) patients treated with HD, using multiple assessments over time.

Two hundred ninety-five outpatients with ESRD treated with HD were recruited from three outpatient dialysis units in Washington D.C. to participate in a prospective cohort study with longitudinal follow-up. Patients were assessed every six months for up to two years using the Beck Depression Inventory (BDI), age, serum albumin concentration, Kt/V, and protein catabolic rate (PCR). A severity index, previously demonstrated to be a mortality marker, was used to grade medical comorbidity. The type of dialyzer with which the patient was treated was noted. Patient mortality status was tracked for a minimum of 20 and a maximum of 60 months after the first interview. Cox proportional hazards models, treating depression scores as time-varying covariates in a univariable analysis, and controlling for age, medical comorbidity, albumin concentration, and dialyzer type and site in multivariable models, were used to assess the relative mortality risk.

The mean (+/- SD) age of our population at initial interview was 54.6 +/- 14.1 years. The mean PCR was 1.06 +/- 0.27 g/kg/day, and the mean Kt/V was 1.2 +/- 0.4 at baseline, suggesting that the patients were well nourished and dialyzed comparably to contemporary U.S. patients. The patients' mean BDI at enrollment was 11.4 +/- 8.1, in the range of mild depression. Patients' baseline level of depression was not a significant predictor of mortality at 38.6 months of follow-up. In contrast, when depression was treated as a time-varying covariate based on periodic follow-up assessments, the level of depressive affect was significantly associated with mortality in both single variable and multivariable analyses.

Higher levels of depressive affect in ESRD patients treated with HD are associated with increased mortality. The effects of depression on patient survival are of the same order of magnitude as medical risk factors. Our findings using both controls for factors possibly confounded with depressive affect in patients with ESRD and time-varying covariate analyses may explain the inconsistent results of previous studies of depression and mortality in ESRD patients. Time-varying analyses in longitudinal studies may add power to defining and sensitivity to establishing the association of psychosocial factors and survival in ESRD patients. The mechanism underlying the relationship of depression and survival and the effect of interventions to improve depression in HD outpatients and general medical inpatients should be studied.