EMIT Cannabinoid Assay: Confirmation by RIA and GC/MS

Abstract

The purpose of this study was to compare the qualitative results obtained by the EMIT Cannabinoid Assay with RIA and two different GC/MS techniques in the analysis of urine specimens for evidence of marijuana use. Reliability of the enzyme immunoassay was assessed from studies on accuracy, precision, and recovery. Precision studies with calibration standards and controls yielded coefficient of variation (C.V.) of 1.0 to 2.8% for assay response rates and approximately 30% in terms of concentration units, illustrating the semi-quantitative nature of the assay. A preliminary recovery study verified that the assay could discriminate effectively between urines apparently devoid of cannabinoids and those spiked at the detection limit, 50 ng/mL. Most samples determined as positive by the enzyme immunoassay yielded the same qualitative results when analyzed by RIA or GC/MS, as well as by EMIT in an independent facility. The confirmatory studies indicated that for routine screening application, the heterogeneity of the EMIT cannabinoid antibody may provide a distinct advantage and that the EMIT assay may be more sensitive than the other methods in detecting cannabinoid metabolites. Analysis of 496 urine samples using the EMIT Cannabinoid Assay suggested at least a casual use of marijuana by approximately 25% of the university student population studied.