Correlations on radioimmunoassay, fluorescence polarization immunoassay, and enzyme immunoassay of cannabis metabolites with gas chromatography/mass spectrometry analysis of 11-nor-Δ 9-tetrahydrocannabinol-9-carboxylic acid in urine specimens

Results obtained from three commercial immunoassay kits, Abuscreen ®, TDx ®, and EMIT ®, commonly used for the initial test of urine cannabinoids (and metabolites) were correlated with the 11-nor-Δ 9-tetrahydrocannabinol-9-carboxylic acid (9-THC-COOH) concentration as determined by GC/MS. Correlation coefficients obtained based on 26 (out of 1359 total sample population) highly relevant samples, are 0.601 and 0.438 for Abuscreen ® and TDx ®. Correlation coefficients obtained from a parallel study on a different set of 47 (out of 5070 total sample population) highly relevant specimens are 0.658 and 0.575 for Abuscreen ® and Emit ®. The immunoassay concentration levels, that correspond to the commonly used 15 ng/ml GC/MS cutoff value for 9-THC-COOH, as calculated from the regression equations are 82 ng/ml and 75 ng/ml for TDx ® and EMIT ® and 120 ng/ml and 72 ng/ml for Abuscreen ® manufactured at two different time periods. The difference of these calculated corresponding concentrations provides quantitative evidence of the reagent specificity differences.