To the Editor: Dr Bliwise and colleagues1 report an association between time of day of hemodialysis
in an elderly cohort of patients with ESRD. It is possible, however, that
the difference in survival between shifts may be even larger than they reported.
The morning cohort had a greater body mass index (BMI). The median dialysis
times between the groups were similar, however, suggesting that the morning
patients likely received a lower dose of hemodialysis. Lower doses of hemodialysis
have been associated with increased mortality.2
Such a trend within this cohort would bias the results toward the null hypothesis
that no difference exists between the groups. Likewise, there was a higher
percentage of black patients in the morning group. Given that black patients
with ESRD tend to have lower hemoglobin values than do white dialysis patients3 and that lower hemoglobin predicts mortality in
ESRD,4 bias would again be introduced toward
the null hypothesis. In an adjusted model, such differences would widen the
disparity in mortality between shifts.
Griffith TF, Coladonato JA, Owen, Jr WF. Does Time of Day of Hemodialysis Affect Survival?. JAMA. 2002;287(10):1262-1264. doi:10-1001/pubs.JAMA-ISSN-0098-7484-287-10-jlt0313