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

Background. The medical risk factors associated with increased mortality in hemodialysis (HD) patients are well known, but the psychosocial factors th at may affect outcome have not been clearly defined. One key psychosocial f actor, depression, has been considered a predictor of mortality, but previo us studies have provided equivocal results regarding the association. We so ught to determine whether depressive affect is associated with mortality in a longitudinal study of end-stage renal disease (ESRD) patients treated wi th HD, using multiple assessments over time. Methods. Two hundred ninety-five outpatients with ESRD treated with HD were recruited from three outpatient dialysis units in Washington D.C. to parti cipate in a prospective cohort study with longitudinal follow-up. Patients were assessed every six months for up to two years using the Beck Depressio n Inventory (BDI), age, serum albumin concentration, Kt/V, and protein cata bolic rate (PCR). A severity index, previously demonstrated to be a mortali ty marker, was used to grade medical comorbidity. The type of dialyzer with which the patient was treated was noted. Patient mortality status was trac ked for a minimum of 20 and a maximum of 60 months after the first intervie w. Cox proportional hazards models, treating depression scores as time-vary ing covariates in a univariable analysis, and controlling for age, medical comorbidity, albumin concentration, and dialyzer type and site in multivari able models, were used to assess the relative mortality risk. Results. The mean (+/- SD) age of our population at initial interview was 5 4.6 +/- 14.1 years. The mean PCR was 1.06 +/- 0.27 g/kg/day, and the mean K t/V was 1.2 +/- 0.4 at baseline, suggesting that the patients were well nou rished 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 m ortality at 38.6 months of follow-up. In contrast, when depression was trea ted as a time-varying covariate based on periodic follow-up assessments, th e level of depressive affect was significantly associated with mortality in both single variable and multivariable analyses. Conclusions. Higher levels of depressive affect in ESRD patients treated wi th HD are associated with increased mortality. The effects of depression on patient survival are of the same order of magnitude as medical risk factor s. Our findings using both controls for factors possibly confounded with de pressive affect in patients with ESRD and time-varying covariate analyses m ay explain the inconsistent results of previous studies of depression and m ortality in ESRD patients. Time-varying analyses in longitudinal studies ma y add power to defining and sensitivity to establishing the association of psychosocial factors and survival in ESRD patients. The mechanism underlyin g the relationship of depression and survival and the effect of interventio ns to improve depression in HD outpatients and general medical inpatients s hould be studied.