More on the false negative rate for EMIT cannabinoids.

We have been following with interest recent reports of false negative EMIT cannabinoid results (1,2). Our laboratory encountered similar problems in two New York City drug abuse proficiency survey samples. Samples 49N2 (February 1989) and 49T5 (August 1989) were spiked at 133 and 150 ng /mL respectively. Both yielded negative cannabinoid EMIT results when tested with the 100-ng/mL cutoff assay kits. Analysis of the two samples by fluorescence polarization immunoassay (FPIA) gave positive cannabinoid results at levels greater than 100 ng/mL. G C / M S quantitation yielded values of 108 and 171 ng /mL for 49N2 and 49T5 respectively (Table I). While this evaluation is inadequate to make general statements on false negative rate for EMIT cannabinoid assay, it does support previous observations that problems exist.