Excessive urinary excretion of isopropyl glucuronide after isopropanol abuse

Ethyl glucuronide (EtG) in urine is considered a marker of alcohol consumption. We present a case of a false-positive immunological EtG screening result due to excessive isopropyl glucuronide excretion in urine of an alcohol-dependent patient with a history of industrial cleaning fluid abuse.

EtG screening was done with the Microgenics DRI EtG enzyme immunoassay on a Beckman Coulter AU680 analyzer according to the testkit instructions. Confirmatory analysis was done by LC-MS/MS for EtG, 1-propyl (syn. n-propyl), 2-propyl (syn. isopropyl), 1-butyl, 2-butyl, and tert-butyl glucuronide. Both methods were validated according to the Guidelines of the Society of Toxicological and Forensic Chemistry (GTFCh, Germany).

EtG screening by immunoassay was positive, approx. 860mg/L or approx. 1540mg/g creatinine (forensic cut-off 0.1mg/L, clinical cut-off 0.5mg/L). LC-MS/MS confirmatory analysis was negative for EtG (<0.05mg/L; forensic cut-off 0.1mg/L), but strongly positive for 2-propyl glucuronide (approx. 1100mg/L or 2000mg/g creatinine; cut-off 0.1mg/L). 1-propyl, 1-butyl, and tert-butyl glucuronide were negative (<0.05mg/L; cut-off 0.1mg/L), 2-butyl glucuronide was 0.1mg/L (cut-off 0.1mg/L).

Consumption of household and industrial chemicals with short chain aliphatic alcohols should be considered a rare but potential source of false-positive EtG immunoassay results. Glucuronides from frequently used short chain aliphatic alcohols, like 1-propanol (syn. n-propanol) and 2-propanol (syn. isopropanol) as the most important disinfectant components, should be included into EtG confirmatory analysis. This will be helpful not only for the assessment of the source for remarkable EtG immunoassay results, it can also contribute to a more specific diagnosis in cases with suspected intoxication by consumer or industrial chemical products. Excessive urinary 2-propyl glucuronide (syn. isopropyl glucuronide) concentrations should be considered a marker of isopropanol intoxication.