Impact of metformin use on the prognostic value of lactate in sepsis.

Objective: The objective of this study is to determine if metformin use affects the prevalence and prognostic value of hyperlactatemia to predict mortality in septic adult emergency department (ED) patients.

Methods: This is a single-center retrospective cohort study. Emergency department providers identified study subjects; data were collected from the medical record.

Patients: Adult ED patients with suspected infection and 2 or more systemic inflammatory response syndrome criteria were included. The outcome was 28-day mortality. The primary risk variable was serum lactate (<2.0, 2.0-3.9, ≥ 4.0 mmol/L) categorized by metformin use; covariates: demographics, Predisposition, Infection, Response, Organ Dysfunction score and metformin use contraindications.

Setting: The study was conducted at an urban teaching hospital; February 1, 2007 to October 31, 2008.

Results: A total of 1947 ED patients were enrolled; 192 (10%) were taking metformin; 305 (16%) died within 28 days. Metformin users had higher median lactate levels than nonusers (2.2 mmol/L [interquartile range, 1.6-3.2] vs 1.9 mmol/L [interquartile range, 1.3-2.8]) and a higher, although nonsignificant, prevalence of hyperlactatemia (lactate ≥ 4.0 mmol/L) (17% vs 13%) (P = .17). In multivariate analysis (reference group nonmetformin users, lactate <2.0 mmol/L), hyperlactatemia was associated with an increased adjusted 28-day mortality risk among nonmetformin users (odds ratio [OR], 3.18; P < .01) but not among metformin users (OR, 0.54; P = .33). In addition, nonmetformin users had a higher adjusted mortality risk than metformin users (OR, 2.49; P < .01). These differences remained significant when only diabetic patients were analyzed.

Conclusions: In this study of adult ED patients with suspected sepsis, metformin users had slightly higher median lactate levels and prevalence of hyperlactatemia. However, hyperlactatemia did not predict an increased mortality risk in patients taking metformin.