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Published:
Journal of Analytical Toxicology,
ISSN 0146-4760,
Volume 26, Number 3, April,
pp. 166-170
Technical Note: Automated Homogeneous Immunoassay Analysis
of Cotinine in Urine
R. Sam Niedbala[1], Nancy Haley[2], Stephanie Kardos[1],
and Keith Kardos[1]
[1]OraSure Technologies, Inc. (OTI), 150 Webster Street, Bethlehem, Pennsylvania
18015-1389 and
[2]Metropolitan Life Insurance Company, Tarrytown, New York
A study was conducted to evaluate
the performance comparison of a homogeneous enzyme immunoassay (EIA) designed
to detect cotinine in urine and carbon monoxide (CO) breath measurements to
determine smoking status. The clinical comparison was done using urine and breath
specimens from 218 volunteers. Urine samples were analyzed by immunoassay and
confirmed by gas chromatography–mass spectrometry (GC–MS). Breath
carbon monoxide was determined by a commercial analyzer. Using cutoffs of 10
ppm for CO and 500 ng/mL for urinary cotinine, the relative sensitivity/specificity
was 93.6%/74.0%. The positive predictive value was 86.8%, and the negative predictive
value was 86.5%. However, comparison of the EIA to GC–MS showed a sensitivity/specificity
of 96.2%/98.4% and a positive predictive value of 99.3%. The EIA was also evaluated
non-clinically for precision, stability, recovery, and interferences. In addition,
the non-clinical evaluation demonstrated coefficients of variation from 0.37
to 1.09% across cotinine concentrations ranging from 0 to 5000 ng/mL. The assay
was found to be highly specific for cotinine and cross-reacted to a limited
degree with 3-hydroxycotinine. Finally, multiple freeze-thaw cycles of urines
containing cotinine showed no degradation of the drug in the specimen when tested
in the EIA. Thus, the EIA tested is a rapid, lab-based test that can reliably
determine cotinine levels and their relation to smoking status. Reproduction
of editorial content of this journal is prohibited without publisher’s
permission.
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