To evaluate the prognostic performance of lactate in septic patients in the emergency department (ED) and investigate how to add lactate to the traditional score systems.

This was a single-centered, prospective, observational cohort study conducted in ED of Beijing Chao-Yang Hospital. The study enrolled adult septic patients admitted to the ED. Arterial lactate was measured in every patient. Acute Physiology and Chronic Health Evaluation (APACHE) II, Sequential Organ Failure Assessment (SOFA), and Mortality in Emergency Department Sepsis (MEDS) scores were calculated on ED arrival. The primary outcome was 28-day mortality.

The average levels of lactate, MEDS, APACHE II, and SOFA were much higher in nonsurvivors than in survivors (P < .001), and they were the independent predictors of 28-day mortality. Area under receiver operating characteristic (AUC) curves of MEDS, APACHE II, SOFA, and lactate were 0.74, 0.74, 0.75, and 0.79, respectively. The AUCs of combination lactate and MEDS, APACHE II, and SOFA were 0.81, 0.81, and 0.82, respectively and were much higher than that of score systems alone (P < .05). The AUCs of modified MEDS, APACHE II, and SOFA were 0.80, 0.80, and 0.81, respectively. The prognostic value of the modified score systems was superior to the original score systems and similar to the combination of the lactate and original score systems.

Lactate is a prognostic predictor in septic patients in the ED, and it may improve the performance of APACHE II, SOFA, and MEDS scores in predicting mortality.