Artifactual elevation of measured plasma L-lactate concentration in the presence of glycolate

Objectives: To determine whether glycolate, a toxic metabolite of ethylene glycol that is chemically similar to lactate, can cause artifactual elevation of measured L-lactate concentrations. Design: Prospective in vitro study. Setting, intensive care unit and chemical pathology laboratory in a university-affiliate hospital. Subjects: Heparinized normal human blood and four commercially available L-lactate analyzers. Interventions: Four analyzers were tested, three of which used L-lactate oxidase and one of which used L-lactate dehydrogenase, Glycolic acid (10 g/L) in saline was added to blood in a series of aliquots, Corresponding plasma L-lactate concentrations and blood pH, Pco(2), and hemoglobin concentrations were measured and base excess was calculated initially and after the addition of each aliquot, One of the two L-lactate oxidase-type analyzers, which was found to show interference, was then used to measure plasma L-lactate and glucose concentrations in blood with glycolic, oxalic, or formic acid added until the base excess was reduced by >15 mmol/L. Measurements and Main Results: Artifactual plasma L-lactate elevations were observed in two analyzers, both of the L-lactate oxidase type. Small concentrations of glycolic acid (causing reductions of base excess of 2-5 mmol/L) were accompanied by artifactual plasma L-lactate elevations of 4-8 mmol/L. Artifactual plasma L-lactate elevations increased with further glycolic acid-induced reductions in base excess. Oxalate and formate did not interfere with plasma L-lactate measurements, and measured plasma glucose concentrations were unaffected by all three acids. Conclusions: Glycotate causes large artifactual elevations in plasma L-lactate measurements by two analyzers in common use, with potential for misdiagnosis of lactic acidosis in ethylene glycol poisoning. A possible cause of the interference is incomplete specificity of the analytical reagent L-lactate oxidase, allowing cross-reaction with glycolate.