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Sensitivity and Specificity of the Cozart Microplate EIA Cocaine Oral Fluid at Proposed Screening and Confirmation Cutoffs

¹ Chemistry and Drug Metabolism, Intramural Research Program, National Institute on Drug Abuse, NIH, 5500 Nathan Shock Dr., Baltimore, MD 21224.

² Cozart Bioscience Ltd., 45 Milton Park, Abingdon, Oxfordshire OX14 4RU, United Kingdom.

^aAuthor for correspondence. Fax 410-550-2468; e-mail mhuestis{at}intra.nida.nih.gov.

Background: Oral fluid is currently being evaluated as an alternative matrix for monitoring illicit drugs in federally mandated workplace drug testing, for addiction treatment programs, and for driving under the influence testing. The sensitivity, specificity, and efficiency of the Cozart® Microplate EIA Cocaine Oral Fluid Kit (COC ELISA) were determined by comparison with gas chromatography–mass spectrometry (GC/MS) results at screening and confirmation cutoffs proposed in the US and UK.

Method: Oral fluid was collected by expectoration after citric acid candy stimulation or with Salivette® neutral cotton swabs or Salivette citric acid-treated cotton swabs before and after cocaine (COC) administration. Specimens (n = 1468) were analyzed with the COC ELISA for screening and with solid-phase extraction followed by GC/MS for confirmation. Three screening cutoffs (10, 20, and 30 µg/L) and four GC/MS cutoffs (2.5, 8, 10, and 15 µg/L COC, benzoylecgonine, and/or ecgonine methyl ester) were evaluated. GC/MS limit of quantification was 2.5 µg/L for all analytes.

Results: COC ELISA interassay imprecision (CV; n = 19) was 16% at 16.7 µg/L and 12% at 81.8 µg/L. With the 2.5, 8, 10, and 15 µg/L GC/MS cutoffs, 59.0%, 54.7%, 52.7%, and 48.7% of the oral fluid specimens were positive, respectively. Sensitivity, specificity, and efficiency were 92.2%, 84.7%, and 88.8%, respectively, for the suggested Substance Abuse and Mental Health Services Administration (SAMHSA) cutoffs and 90.2%, 89.2%, and 89.7% for cutoffs currently used in the UK.

Conclusions: COC ELISA had suitable sensitivity, specificity, and efficiency for identifying COC exposure at both the proposed SAMHSA and UK cutoffs. Sensitivity, specificity, and efficiency were >84% for both cutoffs, but 92 additional true-positive samples were identified with the SAMHSA cutoffs.