Workplace drug testing on urine samples: evidence for improving efficacy of a first-level screening programme

Area of Science:

• Forensic Toxicology
• Occupational Health
• Analytical Chemistry

Background:

• First-level workplace drug testing (WDT) using urine samples shows poor performance in identifying drug users.
• Diluted urine samples pose a challenge, potentially leading to false negatives.
• Previous reports highlight the need for improved WDT methods.

Purpose of the Study:

• To evaluate the impact of creatinine normalization on drug user prevalence in diluted urine samples.
• To identify independent predictors of positive results and sample dilution in WDT.
• To enhance the accuracy of workplace drug testing.

Main Methods:

• Cross-sectional study involving 3080 workers' urine samples analyzed between 2008-2012.
• Immuno-enzymatic screening followed by Gas Chromatography-Mass Spectrometry (GC/MS) confirmation.
• Multivariate logistic regression to identify predictors of positivity and dilution, with creatinine normalization applied to borderline results.

Main Results:

• 51 samples (1.7%) were initially positive for drugs of abuse; 116 (3.8%) were diluted.
• Creatinine normalization increased cannabinoid and cocaine positivity from 1.35% to 2.09% (+55%, p=0.0005).
• Laboratory sample collection was an independent predictor of positivity (OR=2.33) and dilution (OR=1.65).

Conclusions:

• Improving WDT efficacy requires well-controlled pre-analytical procedures.
• Urine creatinine normalization of detected drug concentrations enhances the accuracy of first-level WDT.
• Optimized WDT protocols can better reflect the true prevalence of drug use.