Cross-reactivity of selected compounds in the Abbott TDx cannabinoid assay

Immunoassay procedures, both enzyme immunoassay and radioimmunoassay, continue to be widely used to screen samples for recent marijuana use by analyzing the urine samples for 11-nor-delta 9-tetrahydrocannabinol-9-carboxylic acid (11-nor-delta 9-THC-9-COOH) (the major urinary metabolite of delta 9-tetrahydrocannabinol [delta 9-THC]). Using commercially available immunoassay reagents, the cross-reactivity of the antiserum utilized in Abbott's TDx cannabinoid assay (a fluorescence polarization immunoassay) was evaluated. This cross-reactivity was evaluated against a group of cannabinoids and noncannabinoid phenolic constituents of Cannabis, some cannabinoid metabolites, and other agents that appear in normal urine samples. In general, the antiserum was equally reactive toward 11-nor-delta 9-tetrahydrocannabinol-9-carboxylic acid, its glucuronide, and the corresponding delta 8-isomer, which was the acid moiety utilized in standards and controls of the assay prior to January, 1990. Reduced binding to the antiserum was observed with hydroxylated derivatives of delta 9- and delta 8-THC, and the other cannabinoids, in general, exhibited limited binding potentials toward the antibody. For the noncannabinoid constituents, no binding was observed at the highest concentrations evaluated (40 mg/L).