Serum lactate as a predictor of mortality in patients with infection

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Abstract
Objective To determine the utility of an initial serum lactate measurement for identifying high risk of death in patients with infection. Design and setting Post-hoc analysis of a prospectively compiled registry in an urban academic hospital. Participants Patients with (a) a primary or secondary diagnosis of infection and (b) lactate measurement who were admitted over the 18 months following hospital-wide implementation of the Surviving Sepsis Campaign guideline for lactate measurement in patients with infection and possible severe sepsis. There were 1,177 unique patients, with an in-hospital mortality of 19%. Measurements and results Outcome measures included acute-phase (≤ 3 days) death and in-hospital death. We defined lactate ranges a priori (low, 0.0–2.0; intermediate, 2.1–3.9; high, 4.0 mmol/l or above)—and tested for linear associations with mortality by one-way analysis of variance. We determined sensitivity/specificity, odds ratios, and likelihood ratios for a lactate ≥ 4.0 mmol/l and performed a Bayesian analysis to determine its impact on a full range (0.01–0.99) of hypothetical pretest probability estimates for death. In-hospital mortality was 15%, 25%, and 38% in low, intermediate, and high lactate groups, respectively. Acute-phase deaths and in-hospital deaths increased linearly with lactate. An initial lactate ≥ 4.0 mmol/l was associated with sixfold higher odds of acute-phase death; however, a lactate level less than 4 mmol/l had little impact on probability of death. Conclusions When broadly implemented in routine practice, measurement of lactate in patients with infection and possible sepsis can affect assessment of mortality risk. Specifically, an initial lactate ≥ 4.0 mmol/l substantiallyincreases the probability of acute-phase death.