Laboratory evaluation of the TDx assay for detection of cannabinoids in urine from prison inmates.

The TDx (Abbott Laboratories) and the EMIT-Cobas (Syva Corp. & Roche) techniques for cannabinoid assay were evaluated. Authentic urine samples submitted for narcotics screening were analyzed for cannabinoids. All positive findings were confirmed by an HPLC procedure. The results indicated that the EMIT assay detects a few more positive samples, but also yields a higher rate of unconfirmed positive results compared to the TDx. Those additional "true" positives by EMIT had concentrations of the delta 9-THC-11-carboxylic acid below 10 ng/mL.