Objectives: Serum lactate values in the emergency department (ED) have been associated with mortality in diverse populations of critically ill patients. This study investigates whether serum lactate values measured in the ED are associated with mortality in older patients admitted to the hospital, both with and without infections.Methods: This is a retrospective cohort study performed at two urban teaching hospitals. The study population includes 1,655 older ED patients (age ‡ 65 years) over a 3-year period (2004)(2005)(2006) who had serum lactate measured prior to admission. The presence or absence of infection was determined by review of International Classification of Diseases Ninth Revision (ICD-9) admission diagnosis codes. Mortality during hospitalization was determined by review of inpatient records. Mortality at 30 and at 60 days was determined using a state death registry.Results: In patients with infections, increasing serum lactate values of ‡2.0 mmol ⁄ L were linearly associated with relative risk (RR) of mortality during hospitalization (RR = 1.9 to 3.6 with increasing lactate), at 30 days (RR = 1.7 to 2.6), and at 60 days (RR = 1.4 to 2.3) when compared to patients with serum lactate levels of <2.0 mmol ⁄ L. In patients without infections, a similar association was observed (RR = 1.1 to 3.9 during hospitalization, RR = 1.2 to 2.6 at 30 days, RR = 1.1 to 2.4 at 60 days). In both groups of patients, serum lactate had a greater magnitude of association with mortality than either of two other commonly ordered laboratory tests, leukocyte count and serum creatinine.Conclusions: Higher ED lactate values are associated with greater mortality in a broad cohort of admitted patients over age 65 years, regardless of the presence or absence of infection.ACADEMIC EMERGENCY MEDICINE 2010; 17:260-268 ª 2010 by the Society for Academic Emergency Medicine Keywords: lactic acid, infection, mortality, elderly, older patients, geriatric, emergency A s emergency department (ED) visitors, older adults have the highest admission rate, longest length of stay, and greatest degree of resource utilization of any age group.1 The U.S. population over the age of 65 years is growing, and ED visits for people aged 65-74 years are projected to double from 6.4 million visits to 11.7 million visits per year by 2013. 2,3 Compared to all other age groups, patients over the age of

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