Helpful Only When Elevated: Initial Serum Lactate in Stable Emergency Department Patients with Sepsis Is Specific, but Not Sensitive for Future Deterioration

Background: Early emergency department (ED) identification of septic patients at risk of deterioration is critical. Lactate is associated with 28-day mortality in admitted patients, but little evidence exists on its use in predicting short-term deterioration. Objective: Our aim was to determine the role of initial serum lactate for prediction of short-term deterioration in stable ED patients with suspected sepsis. Methods: We conducted a prospective cohort study of adult ED sepsis patients. Venous lactate was obtained within 2 h of ED arrival. Main outcome was subsequent deterioration (defined as any of the following: death, intensive care admission > 24 h, intubation, vasoactive medications for > 1 h, or noninvasive positive pressure ventilation for > 1 h) within 72 h. Patients meeting any endpoint within 1 h of arrival were excluded. Results: Nine hundred and eighty-five patients were enrolled, of whom 84 (8.5%) met the primary outcome of deterioration. Initial lactate ≥ 4.0 mmol/L had a specificity of 97% (95% confidence interval [CI] 94–100%), but a sensitivity of 27% (95% CI 18–37%) for predicting deterioration, with positive and negative likelihood ratios of 10.7 (95% CI 6.3–18.3) and 0.8 (95% CI 0.7–0.9), respectively. A lower threshold of lactate (≥2.0 mmol/L) had a sensitivity of 67% (95% CI 55–76%) and specificity of 66% (95% CI 63–69%), with corresponding positive and negative likelihood ratios of 2.0 (95% CI 1.7–2.3) and 0.5 (95% CI 0.4–0.7). Conclusions: High ED lactate is predictive of subsequent deterioration from sepsis within 72 h, and may be useful in determining disposition, but low lactate is not effective in screening stable patients at risk of deterioration.