Considerations in the statistical analysis of hemodialysis patient survival

Abstract

The association of hemodialysis dosage with patient survival is controversial. Here, we tested the hypothesis that methods for survival analysis may influence conclusions regarding dialysis dosage and mortality. We analyzed all-cause mortality by proportional hazards and accelerated failure time regression models in a cohort of incident hemodialysis patients who were followed for 9 yr. Both models identified age, race, heart failure, physical functioning, and comorbidity scores as important predictors of patient survival. Using proportional hazards, there was no statistically significant association between mortality and Kt/V (hazard ratio 0.72; 95% confidence interval 0.45 to 1.14). In contrast, using accelerated failure time models, each 0.1-U increment of Kt/V improved adjusted median patient survival by 3.50% (95% confidence interval 0.20 to 7.08%). Proportional hazard models also yielded less accurate estimates for median survival. These findings are consistent with an additive damage model for the survival of patients who are on hemodialysis. In this conceptual model, the assumptions of the proportional hazard model are violated, leading to underestimation of the importance of dialysis dosage. These results suggest that future studies of dialysis adequacy should consider this additive damage model when selecting methods for survival analysis. Accelerated failure time models may be useful adjuncts to the Cox model when studying outcomes of dialysis patients.

Figure 1.

Adjusted ratio of median survival (RS_0.5) as a function of increments in the Kt/V (ΔKt/V) and associated 95% CI (dashed lines) based on estimates of Table 2.

Figure 2.

Survival probabilities of patients according to the PHM (gray line) and the AFTM (thick dashed line) versus the KM estimator (black line) and its associated 95% CI (dotted black lines).

Figure 3.

Smoothed (log) hazard rate as a function of time for Kt/V (solid line) and associated 95% CI.