Urine Exposure Testing
Urine Testing · Urine Testing overview
Urine is the dominant matrix for workplace exposure testing because it is non-invasive, easy to collect at scale and contains validated biomarkers for the majority of substances on HSE's BMGV list and ACGIH's BEI list.
Why urine is the workhorse matrix
Urine integrates exposure across the renal clearance window of each biomarker. For most workplace substances that means it reflects exposure over the preceding 4 to 16 hours, capturing the full shift rather than a single grab. Collection requires no clinical procedure, can be performed on-site by trained staff and is acceptable to most workforces.
Crucially, urine biomarkers reflect absorbed dose across inhalation and dermal routes simultaneously. For skin-notated substances this gives urinary testing a structural advantage over personal air sampling.
Biomarkers and their categories
Urinary biomarkers fall into three classes: the parent substance itself (rare — e.g. urinary mercury), a phase I metabolite (e.g. mandelic acid from styrene), or a phase II conjugate (e.g. S-phenylmercapturic acid from benzene). Each class has different specificity, sensitivity and half-life.
Sampling protocol
Samples are typically collected end-of-shift in 60 ml screw-top universal containers without preservative for organic biomarkers, or in acid-washed containers for metals. The exact last-exposure time is recorded against each sample; results are reported per gram of creatinine (or, where the substance dictates, per litre with specific gravity correction).
Frequently asked questions
How much urine is needed?
Most analytical methods need 20 to 50 ml. A standard 60 ml universal container provides ample material for primary analysis and any required repeat.
Why correct for creatinine?
Creatinine correction normalises for urine dilution, allowing comparison between samples and against reference values that are expressed per gram of creatinine.
Can a single spot urine sample over-estimate exposure?
Yes, particularly for very dilute or very concentrated samples. Creatinine correction or specific gravity correction is essential, and out-of-range samples (creatinine outside 0.3–3 g/l) are usually repeated.
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