Hyperlactatemia: Sensitivity and Specificity
Introduction: From eMedicine: "The normal blood lactate concentration in unstressed patients is 1-0.5 mmol/L. Patients with critical illness can be considered to have normal lactate concentrations of less than 2 mmol/L. Hyperlactatemia is defined as a mild-to-moderate persistent increase in blood lactate concentration (2-5 mmol/L) without metabolic acidosis, whereas lactic acidosis is characterized by persistently increased blood lactate levels (usually >4-5 mmol/L) in association with metabolic acidosis." [http://emedicine.medscape.com/article/768159-overview]
See also Mortality in Sepsis, which is correlated with rising lactate.