• Mitchell, John M.
• Hayes, Eugene D.
• Cone, Edward J.
• Flegel, Ronald

Abstract

Introduction and Aim: When two laboratories analyze hair samples from the same individual for drugs, distinctly different quantitative test results are common. Potential reasons include variable recovery of drugs from the hair, decontamination losses, sensitivity of the method and sample heterogeneity. This study explored the magnitude and causes of these differences in US workplace drug testing.<br/><br/>Materials &amp;Methods: Nine cocaine samples (drug user or contaminated) were analyzed by five US hair testing laboratories with up to five replicates each. In addition, drug user hair and reference materials (Comedical) containing a wider range of analytes were submitted to three of these laboratories.<br/><br/>Results &amp; Discussion: Within-laboratory CVs ranged from 5-22% (4/5 labs ≤11%); however, up to five-fold differences in mean cocaine concentrations between laboratories were observed in cocaine user hair (1159, 2867, 4021, 5708 and 5745pg/mg). This indicates that a homogenous sample can be produced for proficiency testing, but that results are method dependent. References materials sent to three laboratories yielded varied results. One laboratory reported all drugs within the stated reference ranges (100%), another 16 of 21 (76%) and the third none (0%).The differences between laboratories varied between analytes and samples tested, showing the complex interplay between drug incorporation, decontamination, extraction, and analysis. Qualitatively, although some laboratories successfully removed cocaine contamination from soaking in drug solution, no laboratory removed all contamination from drug powder application followed by sweat and shampoo treatments, showing that external contamination cannot be excluded using current guidelines for reporting cocaine in hair.<br/><br/>Conclusions: Determinations of cocaine were reproducible within-laboratory, but results were method dependent. In addition, currently used decontamination protocols might not be sufficient alone to exclude external contamination.<br/>

Topics

• extraction