Performance of Hair Testing for Cocaine Use—Comparison of Five Laboratories Using Blind Reference Specimens.

This article focuses on a comparative study of five commercial hair testing laboratories analyzing cocaine in workplace drug testing, evaluating their bias, precision, selectivity, and decontamination efficiency. Using nine blind hair specimens—including cocaine-positive samples, some contaminated with methamphetamine, and negative samples contaminated with cocaine powder—the study found that all laboratories correctly identified cocaine in drug user specimens but showed substantial interlaboratory variability in quantitative results, with up to fivefold differences likely due to method-dependent factors such as decontamination and extraction protocols. None of the laboratories completely removed external cocaine contamination, indicating current standards may not fully distinguish drug use from contamination; however, metabolite-to-cocaine ratios, particularly of hydroxylated cocaine metabolites, showed potential for differentiating these cases. The findings highlight challenges in standardizing hair drug testing and suggest that proficiency testing programs could improve laboratory performance over time.