Interference by Glycolic Acid in the Beckman Synchron Method for Lactate: A Useful Clue for Unsuspected Ethylene Glycol Intoxication

Abstract

In the differential evaluation of patients with high anion gap metabolic acidosis of unknown origin, lactate determinations are frequently performed. For patients who ingest ethylene glycol (present in antifreeze), the high anion gap metabolic acidosis is the result of the metabolism of ethylene glycol to glycolic acid (1)(2). We encountered unusual lactate results, when measured on the Beckman LX 20 (Beckman Coulter), for two patients who had ingested ethylene glycol. Specifically, the lactate results were suppressed (i.e., no result) with an appended error message, “rate high”. When these specimens were diluted threefold, measurable lactate values were obtained. The Beckman lactate method is based on a lactate oxidase/peroxidase coupled reaction with endpoint determination. The lactate concentration is determined from the absorbance (A) measurement taken after reaction equilibrium has been established. To ensure an equilibrium steady state, a rate measurement is made during the expected steady-state portion of the measurement period. A reaction rate ≥10 m A /min would indicate a nonequilibrium reaction condition and would lead to suppressed results and a “rate high” error flag. We …