Anion Gap is a Predictor of Elevated Serum Lactate in Patients Diagnosed with Sepsis without Shock in the Emergency Department

Objective: To determine whether high anion gap levels predict increased serum lactate >2 mmol/L, and to determine the best AG cut-off point for predicting serum lactate levels greater than 2 mmol/L and greater than 4 mmol/L.Material and Methods: This is a retrospective study among patients with sepsis without shock admitted to the emergency department of a tertiary care, university hospital. Anion gap and serum lactate were collected. Patients’ baseline characteristics and laboratory results were also incorporated to calculate the Sequential (sepsis-related) Organ Failure Assessment (SOFA) score. Analysis of diagnostic accuracy and Receiver Operator Characteristics (ROC) was used to demonstrate the appropriate cut-off point of the anion gap for predicting serum lactate >2 mmol/L.Results: The study included 236 patients. Anion gap >12 mmol/L had a sensitivity of 93.3% (95%CI 88.2-96.6%) and a specificity of 13.7% (95%CI 6.8-23.8%) for predicting serum lactate >2 mmol/L. There was poor discriminative performance of the anion gap to predict serum lactate >2 mmol/L (area under ROC is 0.65; 95%CI 0.58-0.72). In contrast, there was good discriminative performance of the anion gap to predict serum lactate >4 mmol/L (area under ROC 0.83; 95%CI 0.77-0.88). The optimal cut-off point was anion gap > 18 mmol/L, which was good for predicting serum lactate >4 mmol/L.Conclusion: An anion gap >12 mmol/L is not suitable for assessing lactate >2 mmol/L; however, an anion gap >18 mmol/L can predict serum lactate >4 mmol/L in patients with sepsis who had mean arterial pressure (MAP) >65 mmHg.