title: Artifactual elevation of measured plasma L-lactate concentration in the presence of glycolate.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  Prospective in vitro study.
  
  
  METHODS
  Intensive care unit and chemical pathology laboratory in a university-affiliated hospital.
  
  
  METHODS
  Heparinized normal human blood and four commercially available L-lactate analyzers.
  
  
  METHODS
  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, PCO2, 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.
  
  
  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
  Glycolate 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.
authors.affiliation: Division of Anesthesiology and Intensive Care, Royal Brisbane Hospital, Herston, Queensland, Australia.
authors.forename: T J
authors.initials: TJ
authors.lastname: Morgan
authors.forename: C
authors.initials: C
authors.lastname: Clark
authors.forename: A
authors.initials: A
authors.lastname: Clague
mesh_terms: D000140:Acidosis, Lactic / Q000097:blood / Q000139:chemically induced / Q000175:diagnosis; D001784:Blood Gas Analysis; D001786:Blood Glucose / Q000378:metabolism; D003937:Diagnosis, Differential; D019855:Ethylene Glycol / Q000506:poisoning; D005561:Formates / Q000494:pharmacology; D006016:Glycolates / Q000494:pharmacology*; D006454:Hemoglobins / Q000378:metabolism; D006785:Hospitals, University; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007362:Intensive Care Units; D019344:Lactic Acid / Q000097:blood*; D006899:Mixed Function Oxygenases / Q000494:pharmacology; D019815:Oxalic Acid / Q000494:pharmacology; D011446:Prospective Studies
chemical_list: D001786:Blood Glucose; D005561:Formates; D006016:Glycolates; D006454:Hemoglobins; C031149:glycolic acid; C030544:formic acid; D019344:Lactic Acid; D019815:Oxalic Acid; D006899:Mixed Function Oxygenases; C021497:lactate 2-monooxygenase; D019855:Ethylene Glycol