Impact of Lowering Confirmatory Test Cutoff Value in Pre-Enlistment Urine Cannabinoids Screening: About Five Years Experience in the French Gendarmerie

Toxicology Department, Institut de Recherche Criminelle de la Gendarmerie Nationale, Rosny sous bois, France.
Journal of analytical toxicology (Impact Factor: 2.86). 08/2012; 36(8):569-74. DOI: 10.1093/jat/bks067
Source: PubMed


The guidelines for screening of urinary cannabinoids require that all specimens testing positive should be confirmed by gas chromatography-mass spectrometry at a confirmatory test cutoff value of 15 ng/mL of 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (THCCOOH). To assess the impact of lowering the confirmatory test cutoff value on the diagnostic sensitivity and efficiency of a cannabinoid testing program, the results of 986 confirmation analyses of positive screening tests, conducted in the framework of medical fitness examinations prior to enlistment in the French Gendarmerie between January 1, 2005, and December 31, 2009, were retrospectively studied. If the confirmatory test cutoff value of THCCOOH is set at 5 ng/mL instead of 15 ng/mL as recommended by guidelines, the number of confirmed results increases by 25.2%. The positive predictive value of the initial screening test rises from 63.9 to 80.0%. Only one true-positive applicant has appealed. His THCCOOH urinary concentration, which was incompatible with passive cannabis smoke exposure, was confirmed by another laboratory. The use of a confirmatory test cutoff value lower than that recommended significantly increases the diagnostic sensitivity of the screening program for urinary cannabinoids without altering its specificity.

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    • "If the immunoassay is positive, confirmatory testing is required to definitively establish the identity of the THC-COOH metabolite and report the specimen as positive. Confirmatory testing is performed by GC–MS after enzymatic hydrolysis and liquid–liquid extraction according to the method previously published [17]. Among the 26 unconfirmed cannabinoids screening tests – within 172 confirmatory testing carried out in our laboratory between November 1, 2011, and October 31, 2012 – three patients (one female and two males: respectively 47, 36, 48 years old and 65, 69, 105 kg body weight) have confessed to using regularly methoxyisoflavone to the medical officer. "
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