Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (784 page)

   Limitations

   Screening assays are commonly immunoassay based.

   ELISA for blood, serum, plasma

   Target analyte: delta-9-THC

   Cutoff concentration–variable 2–5 ng/mL

   May exhibit significant cross-reactivity with 11-hydroxy-THC, carboxy-THC [THC-COOH]

   Low cross-reactivity with cannabidiol, cannabinol, delta-8-THC

   EIA for urine

   Target analyte: THC-COOH (metabolite)

   Cutoff concentration: 20 ng/mL, 50 ng/mL

   Approximately 50% cross-reactivity with cannabinol, 11-OH-THC

   Confirmation assays are commonly chromatography based regardless of specimen

   Highly glucuronidated–hydrolysis recommended for analysis of urine