Predictors of treatment with dialysis modalities in observational studies for comparative effectiveness research

Abstract

Background: The Institute of Medicine has identified the comparative effectiveness of renal replacement therapies as a kidney-related topic among the top 100 national priorities. Given the importance of ensuring internal and external validity, the goal of this study was to identify potential sources of bias in observational studies that compare outcomes with different dialysis modalities.

Methods: This observational cohort study used data from the electronic medical records of all patients that started maintenance dialysis in the calendar years 2007-2011 and underwent treatment for at least 60 days in any of the 2217 facilities operated by DaVita Inc. Each patient was assigned one of six dialysis modalities for each 91-day period from the date of first dialysis (thrice weekly in-center hemodialysis (HD), peritoneal dialysis (PD), less-frequent HD, home HD, frequent HD and nocturnal in-center HD).

Results: Of the 162 644 patients, 18% underwent treatment with a modality other than HD for at least one 91-day period. Except for PD, patients started treatment with alternative modalities after variable lengths of treatment with HD; the time until a change in modality was shortest for less-frequent HD (median time = 6 months) and longest for frequent HD (median time = 15 months). Between 30 and 78% of patients transferred to another dialysis facility prior to change in modality. Finally, there were significant differences in baseline and time-varying clinical characteristics associated with dialysis modality.

Conclusions: This analysis identified numerous potential sources of bias in studies of the comparative effectiveness of dialysis modalities.

Keywords: bias; comparative effectiveness research; end-stage renal disease; hemodialysis; peritoneal dialysis.

FIGURE 1:

Consort diagram describing the creation of the study cohort.

FIGURE 2:

Summary illustration of utilization of five different dialysis modalities by patients in the cohort relative to the time of initiation of maintenance dialysis. The entire follow-up period for any given patient was divided into 91-day intervals from the day of first dialysis. Each data point in each panel represents the proportion of all patients ever treated with the dialysis modality (viz., peritoneal dialysis for up to 5-years of follow-up) who were undergoing treatment with that particular dialysis modality at that point of time. For example, of the 2653 patients treated with home hemodialysis over the 5-year study period, 25% were being treated with the modality 24 months from the date of first dialysis treatment.

FIGURE 3:

Overlap of availability of different dialysis modalities in the 2217 facilities in 45 states where patients received care. Each circle represents the facilities that offered treatment with any of the six different dialysis modalities, with the size of each circle proportional to the number of facilities. Of the 2217 facilities in 45 states where patients received care, patients received care for TWICHD, PD, less-frequent HD, home HD, frequent HD and NICHD in 2020, 1042, 1219, 520, 671 and 183 facilities, respectively.