Pre & Post-Shift Testing

Urine Testing · Urine Testing overview

Sampling timing must align with biomarker half-life and the relevant BMGV/BEI specification. Pre-shift, end-of-shift and end-of-shift-end-of-week sampling each test a different exposure question.

End-of-shift sampling

End-of-shift sampling is used for biomarkers with a half-life of a few hours — most volatile solvent metabolites. The sample reflects exposure during the just-completed shift. Examples: o-cresol for toluene, methylhippuric acids for xylenes, mandelic acid for styrene, MDA for MDI.

Pre-shift next-morning sampling

For biomarkers with overnight half-lives — for example urinary inorganic mercury, or trichloroacetic acid from trichloroethylene — sampling pre-shift the following morning reflects the previous day's exposure after the rapid excretion phase has finished. This gives a more stable result less affected by within-shift timing.

End-of-shift end-of-week sampling

Substances with biomarker half-lives of multiple days (urinary chromium, urinary cadmium) are sampled at end-of-shift on the last working day of a sequence. The cumulative work-week exposure is reflected, smoothing out daily variability.

Paired pre/post sampling

Pairing pre-shift and post-shift samples is used where background variability is high (non-specific biomarkers such as hippuric acid) or where shift-level uptake needs to be isolated. The within-shift increment is computed per worker.