Xylene Urine Testing

Solvents & VOCs · Solvents & VOCs overview

Xylenes (o-, m-, p-) are metabolised to the corresponding methylhippuric acid isomers, which are quantified in end-of-shift urine as the standard biomarker of occupational xylene exposure.

Biomarker and reference value

Methylhippuric acid isomers (o-MHA, m-MHA, p-MHA) reflect the isomer ratio of the parent exposure. Total methylhippuric acid is reported per gram of creatinine. ACGIH BEI for total methylhippuric acid is 1.5 g/g creatinine end-of-shift.

Unlike hippuric acid (toluene), methylhippuric acid has no significant dietary background, making it a robust biomarker even at moderate exposures.

Application sectors

Spray painting (xylene-based thinners), paint manufacture, lacquer application, laboratory solvent use, surface preparation in MVR body shops, and reinforced plastic lay-up where xylene appears as a styrene co-solvent.

Interpretation

Individual results above the BEI initiate task and control review. Cohort geometric mean above 50% of BEI is the standard review trigger. Stratify by isomer ratio if mixed exposures suggest different control problems on different lines.