The lactate assay (LDH method) used by most labs is the gold standard, while the lactic acid oxidase method used by iSTAT machines produces false positives in the presence of glycolate (a metabolite of ethylene glycol).

If there is lactic acidosis and concern for ethylene glycol poisoning, the serum lactate should be measured using both assays; if there is a difference between the two (lactate gap) then ethylene glycol poisoning is likely present.