RESUMEN

With some exceptions, California Assembly Bill 2188 will preclude the use of ∆9-tetrahydrocannabinol-9-carboxylic acid (Δ9-THC-COOH) as a marker of cannabis use in urinary workplace drug testing. The bill allows for the use of psychoactive cannabis markers, which include Δ9-tetrahydrocannabinol (Δ9-THC) and the metabolite 11-hydroxy-Δ9-tetrahydrocannabinol (11-OH-Δ9-THC). Both analytes are present in urine mainly as conjugated metabolites and will require hydrolysis prior to analysis, but very little is known about expected concentrations in urine. The aim of this study was to report concentrations from two large data sets comprising 1,411 workplace drug testing urine specimens positive by immunoassay (50 ng/mL cutoff) and discuss strategies for using 11-OH-Δ9-THC and/or Δ9-THC to detect cannabis use. Median 11-OH-Δ9-THC and Δ9-THC concentrations were 28-35% and 1.1-1.6% of those of Δ9-THC-COOH and correlations between analytes were observed. To avoid the risk of positives from passive exposure, laboratories could use a cutoff with equivalent sensitivity to cannabis exposure. A 5 ng/mL cutoff for 11-OH-Δ9-THC showed 92% agreement with a 15 ng/mL cutoff for Δ9-THC-COOH, with only 0.9% of specimens being positive only for 11-OH-Δ9-THC. It was not possible to propose an estimated cutoff for Δ9-THC, due to the constraints of the limit of detection used in this study.