Cotinine determination by immunoassays may be influenced by other nicotine metabolites.

Polyclonal rabbit anticotinine antiserum, which can be used for biomonitoring nicotine uptake by the determination of cotinine in body fluids, was checked by a competitive ELISA for its cross-reactivity with nine nicotine metabolites. The highest percentage of relative cross-reactivity (about 30%) was observed with trans-3'-hydroxycotinine, a metabolite which is known to be excreted in 3-fold higher amounts than cotinine in the urine of human smokers. Therefore, it is possible that cotinine determinations performed by immunochemical methods--especially in urine--may yield overestimated cotinine concentrations.