Utilization of a detection level of 25ng/mL for cannabinoids in urine using a CEDIA THCPLUS immunoassay: application of this cut-off to urines of school children.
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 50ng/mL as directed by the AS/NZS 4308:2001 standard. However, the consequent result that we reported, as not detected (<50ng/mL), in many cases did not parallel the pupil's confessed cannabis use. Our laboratory has therefore used a lower cut-off of 25ng/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 49ng/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 25-49ng/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 25ng/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.
Madhavaram
Hima
H
LabPlus, Auckland City Hospital, Auckland, New Zealand. himam@adhb.govt.nz
Couch
Ronald A F
RA
D000293:Adolescent; D002186:Cannabinoids / Q000652:urine*; D002648:Child; D053593:Forensic Toxicology; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D007118:Immunoassay / Q000295:instrumentation*; D008385:Marijuana Smoking; D009520:New Zealand; D015813:Substance Abuse Detection / Q000295:instrumentation
D002186:Cannabinoids