Elevated lactate in ethylene glycol poisoning: True or false?

Background: There have been an increasing number of reports on false increase of lactate in ethylene glycol poisoning. We recently encountered two cases of ethylene glycol poisoning with very high blood lactate concentrations on ABL blood gas analyzers.

Methods: Patient plasma lactate concentrations were measured on different chemistry instruments in addition to ABL analyzer. Serum ethylene glycol and glycolic acid were also determined. Lactate values were determined from samples spiked with various amounts of glycolic acid.

Results: In case 1, all the chemistry instruments produced similar lactate results compared to that by ABL analyzer whereas in case 2, the lactate on the ABL was dramatically elevated compared to that from all the chemistry analyzers. There was no glycolic acid detected in case 1 but high glycolic acid was obtained in case 2. Increased concentrations of glycolic acid resulted in a significant positive interference on lactate measurements on the ABL analyzer but none on other instruments.

Conclusions: False increase of blood lactate by blood gas analyzers may occur but true increase of lactate can also be observed in ethylene glycol poisoning. Elevated lactate concentrations on blood gas analyzers should be confirmed by a chemistry analyzer in the differential diagnosis of ethylene glycol poisoning.