Acute Inhaled Xylene Poisoning Confirmed by Methylhippuric Acid Urine Test

Xylene is a commonly used toxic volatile organic solvent. Diagnosis of acute xylene poisoning is limited by the lack of a readily available analytic assay. Methylhippuric acid, a metabolite of xylene excreted in the urine, is used for biomonitoring occupational exposures to xylene. We report two cases of acute occupational poisoning from xylene inhalation suggested by determination of high urinary methylhippuric acid. Two 21 and 23 years old healthy male adults collapsed after inhaling an unknown paint thinner during painting. On admission to the emergency department, they were confused and agitated, without hemodynamic or respiratory impairment. Admission urinary methylhippuric acid determined by HPLC with UV detector were 2.57 and 2.68 g/g creatinine (Biologic Exposure Index, BEI, 1.5 g/g creatinine). Urinary hippuric acid was below the previously used BEI for toluene. Mild increases in alanine aminotransferase (80 U/L) and aspartate aminotransferase (71 U/L) were found 12 hours after exposure, returning to normal after 24 hours. The patients gradually regained full consciousness within 24 hours and discharged after 48 hours' observation without any sequelae. High urinary methylhippuric acid concentrations suggested the diagnosis of acute xylene poisoning following its inhalation. Diagnosis in previous reports of acute xylene poisonings relied on history and clinical manifestations. Urinary methylhippuric acid assay is specific and available in special laboratories. It is suggested to determine urinary methylhippuric acid together with metabolites of other widely available organic solvents (e.g., hippuric acid, trichloroacetic acid) whenever unintentional exposure or abuse of volatile organic compounds is suspected.