Can urinary phenylglyoxylic acid indicate styrene or ethylbenzene exposure?

Urinary phenylglyoxylic acid (PGA) is an established urinary metabolite used in occupational biomonitoring for exposure to both styrene and ethylbenzene. Its principal value is identifying relatively recent solvent exposure, not determining the unique source of that exposure.

Clinical and occupational monitoring evidence

• For styrene, ACGIH biological exposure monitoring uses the end-of-shift urinary sum of mandelic acid (MA) plus PGA, normalized to creatinine. The cited biological exposure index is 400 mg/g creatinine, corresponding to a styrene time-weighted average of 20 ppm.
• For ethylbenzene, end-of-shift urinary PGA has correlated with measured workplace exposure in solvent workers (r = 0.6–0.7), supporting its use as an exposure biomarker, although with less specific validation than the combined styrene index.

Metabolic interpretation and timing

• Both styrene and ethylbenzene generate urinary PGA and MA. This shared metabolism explains why PGA is useful for detecting exposure but cannot, by itself, identify whether styrene or ethylbenzene was responsible.
• Sampling time materially affects interpretation: urinary MA and PGA generally peak about 3 hours after exposure, and PGA’s reported urinary elimination half-life is approximately 8–10.5 hours. Results therefore primarily reflect recent exposure.
• Standardized end-of-shift collection and combined MA+PGA measurement improve comparability and interpretation.

Practical implications

• A PGA result should be interpreted alongside MA, work history, likely mixed-solvent exposures, and—when available—workplace air monitoring. A single isolated PGA measurement is not a durable marker of remote exposure or a source-specific diagnostic test.

Bottom line

• Urinary PGA is a scientifically supported biomarker of recent styrene and ethylbenzene exposure, especially in occupational settings; however, it is not chemically source-specific, so combined MA+PGA testing and exposure context are essential.