Serum lactate upon emergency department arrival as a predictor of 30-day in-hospital mortality in an unselected population

BACKGROUND Despite of numerous evidences that elevated serum lactate levels were associated with unfavorable outcomes, there have been no study demonstrated an optimal cutoff of serum lactate in unselected patients. This study was aimed to evaluate the prognostic property of lactate, and to identify a cutoff of serum lactate level for predicting 30-day in-hospital mortality among unselected patients presenting to the emergency department (ED). METHODS We performed a retrospective observational study from January 2010 to December 2016. 61,151 patients were used for propensity score analysis after exclusion. 14,015 patients who underwent lactate test at ED arrival were enrolled for final analysis. RESULTS The average treatment effect (ATE) of carrying out a lactate test on 30-day in-hospital mortality was 0.53% (adjusted odds ratio (OR) = 1.013, p = 0.19; 95% confidence interval (CI), 0.997-1.013). Adjusted OR of serum lactate calculated from multivariable analysis was 1.09 (p < 0.001; 95% CI, 1.07-1.10). The area under a ROC curve (AUC) of serum lactate was 0.711 (p < 0.001; 95% CI, 0.703-0.718). The sensitivity, specificity, and positive and negative predictive values for the cutoff > 2.6 mmol/L were 56.7%, 74.3%, 20.8%, and 93.5%, respectively. Mortality of the high-lactate group (> 2.6 mmol/L) was significantly higher than that of the low lactate group (≤ 2.6 mmol/L) (20.8% vs. 6.5%, difference = 14.3%, p < 0.01; 95% CI, 13.0% - 15.7%). CONCLUSIONS A serum lactate level > 2.6 mmol/L predicted 30-day in-hospital mortality in unselected patients who arrived to the ED and were admitted to the hospital. Additionally, serum lactate test in the ED could be an effective screening method for identifying low risk patients.