A False Positive Gamma-Hydroxy Butyric Acid Urine Screening in a Patient with High Anion Gap Metabolic Acidosis due to Ethylene Glycol Poisoning.

A young woman with a history of several suicide attempts was admitted to the hospital after suspicion of a new intoxication without definite identification of the causing agent. The patient had a high anion gap metabolic acidosis (HAGMA) with respiratory compensation, a lactate gap and an osmolar gap at admission. Initial toxicological screening showed no abnormalities except for a weak positive gamma-hydroxy butyric acid (GHB) enzymatic screen in urine. This finding could not be confirmed with chromatographic analysis nor be explained by the presence of known cross reacting substances like ethanol. In this case, the falsely elevated urinary gamma-hydroxy butyric acid screening was caused by the ingestion of ethylene glycol. To confirm that the interference was due to ethylene glycol or its metabolites, we performed a spiking experiment. Cross reactivity was linked to ethylene glycol and was low in our experiments (0.1-0.2%). Substantial amounts of ethylene glycol are required to slightly elevated GHB results, depending on the endogenous cutoff used. We can conclude that ethylene glycol can give rise to falsely elevated urinary gamma-hydroxy butyric acid levels at ethylene glycol concentrations that are typically found in intoxications.