Prognostic value of plasma lactate levels in a retrospective cohort presenting at a university hospital emergency department

OBJECTIVES The prognostic value of lactate in the setting of an emergency department (ED) has not been studied extensively. The goal of this study was to assess 28-day mortality in ED patients in whom lactate was elevated (≥4.0 mmol/L), <4.0 mmol/L or not determined and to study the impact of the underlying cause of hyperlactatemia, that is, type A (tissue hypoxia) or type B (non-hypoxia), on mortality. DESIGN Retrospective study. SETTING A secondary and tertiary referral centre in the Netherlands. MATERIALS AND METHODS All internal medicine patients with hyperlactatemia (≥4.0 mmol/L) at the ED between January 2011 and October 2014 were included in this study. Samples of patients with lactate levels <4.0 mmol/L and of patients in whom no lactate was measured were included as a reference. RESULTS In 1144 of 19 822 patients (5.8%), lactate was measured. Hyperlactatemia (n=197) was associated with a higher 28-day mortality than in those with lactate <4.0 mmol/L (40.6% vs 18.5%; p<0.001) and in those without lactate measurements (9.5%). Type A hyperlactatemia, present in 84% of those with hyperlactatemia, was associated with higher mortality than type B hyperlactatemia (45.8% vs 12.5%, p=0.001). CONCLUSIONS This study demonstrates that the prognostic value of lactate depends largely on the underlying cause and the population in whom lactate has been measured. Prospective studies are required to address the true added value of lactate at the ED.