Relative hyperlactatemia and hospital mortality in critically ill patients: a
retrospective multi-centre study
In healthy individuals there is a continuous cycle of lactate production and metabolism,
which ensures that blood lactate concentrations are normally low [1, 2]. Higher blood lactate
concentrations occur when lactate production exceeds clearance, when clearance capacity is
decreased or more frequently when both occur simultaneously [3, 4]. Elevated blood lactate
concentrations above the accepted “normal” reference range (absolute hyperlactataemia) are
common and associated with increased hospital mortality in the critically ill [5-12]. Their
usefulness in identifying critically ill patients at higher risk of death has led to the adoption of
lactate measurement in most blood gas analyzers and the frequent measurement of lactate in the
critically ill.
While the normal lactate concentration in unstressed individuals is 1.0±0.5 mmol.L-1 [1, 2],
patients with critical illness are considered to have normal lactate levels at concentrations of less
than 2 mmol.L-1 [13]. Furthermore, this 2 mmol.L-1 cut off may be considered to be
conservative threshold as some have suggested that level of up to 4 mmol.L-1 is within the
normal limits [14].
However, it is unknown whether a higher blood lactate concentration within the current
reference range (relative hyperlactataemia) might also be associated with increased hospital
mortality. This knowledge would be clinically important because the currently used upper
reference limit for lactatemia may fail to identify many patients who are at higher risk of death.
We hypothesized that higher blood lactate concentrations within the reference range
would be associated with an increased risk of hospital death and investigated the relationship
between ICU admission, maximal and time-weighted blood lactate concentrations and hospital
mortality in a large cohort of critically ill patients.
