Lactate - Arterial and Venous Agreement in Sepsis: a prospective observational study

BackgroundSepsis is a common condition in the emergency department (ED). Lactate measurement is an important part of management: arterial lactate (A-LACT) measurement is the gold standard. There is increasing use of peripheral venous lactate (PV-LACT); however, there is little research supporting the interchangeability of the two measures.If PV-LACT has good agreement with A-LACT, it would significantly reduce patient discomfort and the risks of arterial sampling for a large group of acutely unwell patients, while allowing faster and wider screening, with potential reduced costs to the healthcare system.ObjectiveThe aim of this study is to determine the agreement between PV-LACT and A-LACT in septic patients attending the ED.MethodsWe carried out a prospective observational cohort study of 304 consented patients presenting with sepsis to a single UK NHS ED (110000 adult attendances annually) taking paired PV-LACT and A-LACT. Bland-Altman analysis was carried out to determine agreement. Receiver operating characteristic curves and 2x2 tables were constructed to explore the predictive value of PV-LACT for A-LACT.ResultsThe mean difference (PV-LACT-A-LACT) is 0.4mmol/l [95% confidence interval (CI): 0.37-0.45], with 95% limits of agreement from -0.4 (95% CI: -0.45 to -0.32) to 1.2 (95% CI: 1.14-1.27). A PV-LACT of at least 2mmol/l predicts an A-LACT of at least 2 with 100% sensitivity (95% CI: 89-100%) and 83% specificity (95% CI: 77-87%).ConclusionThis study is the largest comparing the two measurements, and shows good clinical agreement. We recommend using PV-LACT in the routine screening of septic patients. A PV-LACT less than 2mmol/l is predictive of an A-LACT less than 2mmol/l.