Detection and Interpretation of Lysergic Acid Diethylamide Results by Immunoassay Screening of Urine in Various Testing Groups

A total of 2259 urine samples were assayed for lysergic acid diethylamide (LSD) using radioimmunoassay (RIA, Coat-a-Count, Diagnostics Products) and a premarket cloned enzyme donor immunoassay (CEDIA, Boehringer Mannheim). Urine samples were obtained from patients admitted to the emergency room, patients in drug rehabilitation programs, and adults and juveniles in criminal probation programs. An overall incidence of positive results was 0.80% for CEDIA (500-pg/mL cutoff) and 0.89% and 0.18% for RIA at cutoffs of 250 and 500 pg/mL, respectively. Of the CEDIA-positive samples, only 17 and 11% were positive by RIA at 250 and 500 pg/mL, respectively, whereas among RIA-positive samples, only 10% of those > 250 pg/mL and only 25% of those > 500 pg/mL were positive by CEDIA. Moreover, only 2 of 25 of samples positive by one of these screening assays were confirmed by gas chromatography-mass spectrometry (GC-MS). It is likely that discrepancies in results between immunoassays are due to differences in antibody specificities used to detect LSD metabolites. In addition, immunoassays may be more sensitive than GC-MS for detecting LSD use as current confirmation assays are targeted towards detection of the parent drug only. The interpretation of results for LSD analysis must be made with knowledge of the limitations for each assay.