Declining Mortality in Patients with Acute Renal Failure, 1988 to 2002 Sushrut S. Waikar,* Gary C. Curhan,* Ron Wald, † Ellen P. McCarthy, ‡ and Glenn M. Chertow § *Renal Division and Channing Laboratory, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts; † Division of Nephrology, Tufts-New England Medical Center, Boston, Massachusetts, and Division of Nephrology, University of Toronto, Toronto, Ontario, Canada; ‡ Division of General Medicine and Primary Care, Beth Israel-Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts; and § Division of Nephrology, Departments of Medicine and Epidemiology and Biostatistics, University of California San Francisco, San Francisco, California Despite improvements in intensive care and dialysis, some experts have concluded that outcomes associated with acute renal failure (ARF) have not improved significantly over time. ARF was studied in hospitalized patients between 1988 and 2002 using the Nationwide Inpatient Sample, a nationally representative sample of discharges from acute-care, nonfederal hospitals. During a 15-yr period, 5,563,381 discharges with ARF and 598,768 with ARF that required dialysis (ARF-D) were identified. Between 1988 and 2002, the incidence of ARF rose from 61 to 288 per 100,000 population; the incidence of ARF-D increased from 4 to 27 per 100,000 population. Between 1988 and 2002, in-hospital mortality declined steadily in patients with ARF (40.4 to 20.3%; P < 0.001) and in those with ARF-D (41.3 to 28.1%; P < 0.001). Compared with 1988 to 1992, the multivariable-adjusted odds ratio (OR) of death was lower in 1993 to 1997 (ARF: OR 0.62, 95% confidence interval [CI] 0.61 to 0.64; ARF-D: OR 0.63, 95% CI 0.59 to 0.66) and 1998 to 2002 (ARF: OR 0.40, 95% CI 0.39 to 0.41; ARF-D: OR 0.47, 95% CI 0.45 to 0.50). The percentage of patients who had ARF with a Deyo-Charlson comorbidity index of 3 or more increased from 16.4% in 1988 to 26.6% in 2002 (P < 0.001). This study provides evidence from an administrative database that the incidence of ARF and ARF-D is rising. Despite an increase in the degree of comorbidity, in-hospital mortality has declined. J Am Soc Nephrol 17: 1143–1150, 2006. doi: 10.1681/ASN.2005091017 A cute renal failure (ARF) is one of the most common and serious complications of hospitalized patients. Our understanding of the epidemiology of ARF has been limited by the lack of a uniform definition of ARF and the preponderance in the literature of relatively small, mostly sin- gle-center studies. As a result, estimates of the in-hospital mor- tality associated with ARF have ranged widely. Even among studies of a homogeneous group of patients such as those who were admitted to the intensive care unit (ICU) with ARF that required dialysis (ARF-D), mortality rates have ranged from 44 to 79% (1,2). Little information exists on secular trends in the epidemiol- ogy of ARF. There are several reasons to suspect that ARF may be more common now than previously: The increasing age and comorbidities of the hospitalized population (3); an increase in the prevalence of risk factors for ARF, such as chronic kidney disease (4) and diabetes (5); and more widespread use of intra- venous contrast for cardiovascular procedures (6). Whether the outcomes of patients with ARF have improved in recent years along with advances in critical care medicine and dialysis technologies is controversial. Many reviews of ARF have adopted a pessimistic view, citing studies that were performed during different time periods to argue that mortality rates that are associated with ARF have not changed over several decades (7–9). A systematic review of 80 studies of ARF involving 15,897 patients between 1970 and 2004 concluded that mortality rates have remained unchanged (10). The hand- ful of studies that have specifically examined mortality rates of ARF over time have been small (N  710) and have yielded conflicting conclusions (11–17). Using the Nationwide Inpatient Sample (NIS), a large and nationally representative administra- tive database of hospital discharges from 1988 to 2002, we attempted to determine secular trends in the incidence, in- hospital mortality, length of stay (LOS), and disposition (dis- charge to home versus posthospital care) for patients with ARF and ARF-D. Materials and Methods Data Source The NIS is the largest all-payer administrative database of hospital- izations in the United States. From 1988 to 2002, the NIS has provided data annually from 5 to 8 million inpatient stays. The NIS captures patient-level data from a 20% stratified probability sample of US hos- pitals from states that participate in the Healthcare Cost and Utilization Project. Included in the NIS are teaching and nonteaching hospitals, Received September 29, 2005. Accepted January 15, 2006. Published online ahead of print. Publication date available at www.jasn.org. Address correspondence to: Dr. Sushrut S. Waikar, Channing Laboratory, Brigham and Women’s Hospital, 181 Longwood Avenue, Boston, MA 02115. Phone: 617-525-2740; Fax: 617-525-2008; E-mail: swaikar@partners.org Copyright © 2006 by the American Society of Nephrology ISSN: 1046-6673/1704-1143