Contraception in primary care--embracing the Institute of Medicine challenge.

n engl j med 365;25 nejm.org december 22, 2011 2438 lations and the actual day of the week when dialysis was performed in our study population. In the U.S. population overall, the variability in mortality is much smaller than we observed among typical patients receiving hemodialysis. For example, among 2,428,343 deaths in 2007, the proportions occurring on Sunday through Saturday were 14.2%, 14.5%, 14.2%, 14.2%, 14.2%, 14.4%, and 14.5%, respectively.1 Within the data set for our primary study report, outcome patterns were similar in the Monday, Wednesday, and Friday (MWF) and Tuesday, Thursday, and Saturday (TTS) populations in the sense that event rates were highest on Mondays in the MWF group and on Tuesdays in the TTS group. For example, in the MWF group, the annualized Sunday through Saturday mortality was 16.1, 21.8, 17.4, 18.8, 17.6, 18.3, and 18.0 per 100 person-years, as compared with 17.0, 22.5, 17.7, 19.8, 19.1, and 18.0 in the TTS group. Corresponding cardiovascular event rates were 23.2, 44.7, 28.4, 33.8, 25.1, 29.7, and 17.1 in the MWF group and 17.7, 33.9, 43.4, 26.1, 30.6, 22.7, and 25.7 in the TTS group. Hence, patterns of mortality appear to be more related to the interdialytic interval than to the actual day of the week. Only 260 patients (0.8%) in the data set underwent dialysis more frequently than three times per week, and it is difficult to gauge scheduling from the dates of predialysis blood urea levels. Of the 137 deaths observed, the proportions from Sunday through Saturday were 13.1%, 13.9%, 11.0%, 18.3%, 15.3%, 10.2%, and 18.3%. Hence, there was no evidence of a Monday effect in this small subgroup. Variability appears to be less marked in the U.S. population receiving peritoneal dialysis. For example, unpublished data from the United States Renal Data System for 2007 showed that from Sunday to Saturday, the proportions of deaths in the prevalent peritoneal dialysis populations were 13.3%, 14.5%, 14.3%, 14.5%, 14.3%, 14.8%, and 14.3%.