Biological Monitoring Sampling Strategy

Exposure Indices · Exposure Indices overview

Sampling strategy is the design decision that most influences whether a biological monitoring programme can defensibly conclude that controls are adequate. It covers cohort selection, sample timing, sample size and analytical method.

Cohort and SEG selection

Similar Exposure Groups (SEGs) are defined by task, location and substance — not by job title. Workers in a single SEG are expected to have lognormally distributed exposures with similar geometric mean. Each SEG is sampled independently.

Sample size

For routine verification a minimum of six samples per SEG is typical, scaling to ten or more where exposure variability is high or where the reference value is close to the action level. EN 689 statistical methods are commonly applied.

Sample timing

Timing aligns with biomarker half-life and the matrix specified by the BMGV/BEI. End-of-shift, pre-shift next-morning, and end-of-shift-end-of-week are the three primary timing windows. The wrong timing window invalidates the result.

Matrix and method

Urine is preferred where validated; blood is used for protein-bound metals; exhaled air for very volatile parent compounds. Methods are UKAS-accredited and run by a laboratory participating in a recognised external proficiency scheme.