Lowering the federally mandated cannabinoid immunoassay cutoff increases true-positive results

Proposed changes to the Health and Human Services Guidelines for forensic urine drug testing will lower the required cannabinoid immunoassay cutoff concentration from 100 to 50 μg/L. We investigated the effect of this change on the sensitivity, specificity, and efficiency of eight cannabinoid immunoassays: Syva Emit(®) d.a.u.(TM) 100; Syva Emit II 100; Syva Emit d.a.u. 50; Syva Emit II 50; Roche Abuscreen(®) Online(TM); Roche Abuscreen radioimmunoassay; Diagnostic Reagents(®); and Abbott ADx(®). All specimens also were assayed by gas chromatography/mass spectrometry. Lowering the cutoff concentration from 100 to 50 μg/L increased efficiencies and sensitivities for all immunoassays, with minor decreases in specificity (1.0- 2.6%). There was a 23.2-53.6% increase in the number of true-positive specimens identified. Thus, lowering the cannabinoid immunoassay cutoff concentration from 100 to 50 μg/L resulted in detection of a substantial number of additional true-positive specimens, with an accompanying small increase in unconfirmed positive results.