Utilization of a detection level of 25
ng/mL for cannabinoids in urine using a CEDIA® THCPLUS immunoassay: Application of this cut-off to urines of school children
Abstract
Cannabis is the most widely used illicit drug in New Zealand. About 4 years ago schools in New Zealand began introducing drug programmes in order ascertain a pupil's likely cannabinoid use. Our toxicology laboratory screened such specimens for the presence of cannabinoids, using CEDIA® immunoassay, at a cut-off of 50
ng/mL as directed by the AS/NZS 4308:2001 standard. However, the consequent result that we reported, as not detected (<50
ng/mL), in many cases did not parallel the pupil's confessed cannabis use.
Our laboratory has therefore used a lower cut-off of 25
ng/mL, by this immunoassay. We use this cut-off only for non-evidential analyses.
Stored specimens were analysed over two time periods. Initially 2359 urine samples were screened for cannabinoids. 130 of these specimens had a value between 25 and 49
ng/mL and 60 of this group were randomly selected for confirmation by GC–MS. In all the 60 specimens, the presence of THCCOOH was confirmed. A further 760 specimens were collected over a later time period. Of these, 48 specimens had an immunoassay value of 25–49
ng/mL and all 48 specimens were confirmed positive for THCCOOH by GC–MS.
This study indicates that the CEDIA® THCPLUS immunoassay can be used to screen for the presence of urinary cannabinoids using a 25
ng/mL cut-off. Use of such a cut-off will limit the occurrence of false negative cannabinoid screening results.
For school children a lower cut-off may be important, as consequent remedial action, following a positive immunoassay result, may limit the adverse outcomes such as dependence and impairment of achievements as suggested in a New Zealand study by Fergusson and Joseph.
Keywords: Cannabinoids, Urine, Cut-off value, Children
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PII: S0379-0738(10)00062-9
doi:10.1016/j.forsciint.2010.02.010
© 2010 Elsevier Ireland Ltd. All rights reserved.
