Low baseline serum creatinine concentration predicts mortality in critically ill patients independent of body mass index

OBJECTIVE: Malnutrition and low muscle mass reduce the ability of patients to fight critical illness. Low serum creatinine is a better surrogate marker of low muscle mass than a low body mass index and has been associated with poor outcome in some patient populations. We hypothesized that low baseline serum creatinine would predict poor outcome in the critically ill. DESIGN: In this retrospective cohort study, data including age, gender, race, postoperative status, and Acute Physiology and Chronic Health Evaluation (APACHE) III scores were collected from the institutional APACHE III database. Baseline serum creatinine levels and body mass index were collected from the hospital laboratory database. The main outcomes measured were hospital mortality and intensive care unit length of stay. PATIENTS: Consecutive critically ill patients >18 yrs of age admitted to three ICUs from January 2003 to December 2006, excluding those who denied research authorization, did not have a baseline serum creatinine measured, were pregnant at the time of intensive care admission, had a history of chronic renal replacement, were in intensive care for <12 hrs, or were admitted for low-risk monitoring only. SETTING: Three intensive care units of two tertiary care hospitals. RESULTS: Of 11,291 patients who met the inclusion criteria, 1185 (10%) died in the hospital. Of the patients, 54% were male and 90% were white, with a mean age (+/-sd) of 63 +/- 17 yrs. Median body mass index was 27.3 (interquartile range [IQR], 23.5-32.1), median APACHE III score was 53 (IQR, 38-69), and median baseline serum creatinine was 1.1 (IQR, 0.9-1.4). When adjusted for APACHE III-predicted mortality, age, gender, postoperative state, and body mass index, low baseline creatinine was associated with increased mortality in a dose-response manner: odds ratio (OR) 2.59 (95% confidence interval [CI], 1.82-3.61) for baseline creatinine < or =0.6 mg/dL (p < .001) and OR 1.28 (95% CI, 1.03-1.60) for baseline creatinine 0.6-0.8 mg/dL (p = .023). Adjusted intensive care length of stay in survivors was 0.48 days (95% CI, 0-0.98) longer for patients with baseline creatinine < or =0.6 mg/dL (p = .058). CONCLUSION: Low baseline serum creatinine concentrations increase the risk of mortality in critically ill patients.