Measurement uncertainty in urine drug analysis: A comparison of ISO/TS 20914 and GUM/Eurachem approaches.

BACKGROUND

Urine drug screening and confirmation tests play a critical role in forensic and clinical toxicology applications. This study evaluates and methodologically compares ISO/TS 20914 and GUM/EURACHEM approaches for estimating measurement uncertainty of multiple drugs of abuse analyzed by LC-MS/MS.

METHODS

Seventeen target analytes, including drugs of abuse and their metabolites, were analyzed by LC-MS/MS, and measurement uncertainty was estimated using calibration data, one-year internal quality control results, and external quality assessment data according to both GUM/EURACHEM and ISO/TS 20914 approaches (95% confidence, k = 2).

RESULTS

The GUM/EURACHEM approach yielded higher uncertainty estimates than ISO/TS 20914 for all analytes, primarily due to calibration and preparation components. The highest expanded uncertainty was observed for buprenorphine and heroin (17.7%) and the lowest for MDEA (5.9%). Relative differences (%ΔU) consistently favored the ISO/TS 20914 approach, with the calibration curve being the main contributor in the GUM/EURACHEM model.

CONCLUSIONS

The ISO/TS 20914 approach provides a practical and sustainable framework for routine high-throughput toxicology laboratories, whereas the GUM/EURACHEM approach is more suitable for detailed uncertainty assessment during method development and validation. Measurement uncertainty should be considered in result interpretation, particularly for samples near decision thresholds, where it may influence classification and impact forensic and clinical decision-making.