Screening for cannabinoids in blood using EMIT: concentrations of delta-9-tetrahydrocannabinol in relation to EMIT results.

The EMIT d.a.u. cannabinoid assay of methanolic extracts of blood was found to be usable as a screening method in cases of suspected impairment by cannabis, when delta-9-tetrahydrocannabinol (THC) was analysed in the subsequent assay. A prerequisite is that the blood sample is taken some time after cannabis smoking. When a cut-off limit corresponding to 50 nM delta-9-tetrahydrocannabinol carboxylic acid (17 ng/ml) was used, 86% of the EMIT positive blood samples contained THC concentrations above the cut-off limit of 1 nM (0.3 ng/ml). A high EMIT result gave a high probability of finding a high THC concentration in the subsequent confirmation analysis.