Phencyclidine blood concentrations in DRE cases.

Phencyclidine (PCP) concentration was measured in blood obtained from 259 individuals over a two-year period subsequent to Drug Recognition Expert (DRE) evaluation by the Maryland State Police. The purpose of this study was to evaluate the accuracy of the DRE in the identification of PCP-related impairment using the presence of PCP in blood to confirm drug use and to test for a correlation between PCP concentrations in blood and impairment as indicated by DRE evaluation. Of the 259 cases evaluated, 124 were identified as positive for PCP based on DRE evaluation, 130 were positive for PCP based on toxicological analysis, and 56 of the 124 were identified as positive for PCP only by DRE and subsequently confirmed to contain only PCP. The mean PCP concentration for those cases in which only PCP was identified by both DRE and toxicology was 51 ng/ml (standard deviation, 26 ng/mL) with a range of values of 12-118 ng/mL. Although no correlation was determined between PCP concentration and behavior, it is clear that, even at concentrations as low as 12 ng/mL, PCP-induced behavioral effects are measurable by DRE evaluation. This study also revealed that despite a low false-positive rate (3%) of detection of PCP use by the DRE, the false-negative rate of 8% supports the conclusion that the toxicological analysis of blood specimens for PCP provides the necessary, objective corroboration of the DRE's opinion concerning impairment.