Immunoassay screen to for qualitative detection of cotinine in urine.

Tobacco smoking or passive inhalation of tobacco smoke results in the absorption of nicotine through the lungs and mucus membranes of the mouth. When nicotine is absorbed, it is readily metabolized into cotinine as its major metabolite. Cotinine is detectable in the urine of smokers even several days after the termination of smoking. Several methods, including the measurement of thiocyanate, carbon monoxide and cotinine, can be used to determine an individual’s smoking status. Measurement of either carbon monoxide or thiocyanate can give a false indication of tobacco use, as they may come from other environmental sources. 

Cotinine, on the other hand, can only be derived from the metabolism of nicotine, and is therefore the best indicator of smoking status. The cotinine screening assay is based on competition between cotinine labeled with glucose-6-phosphate dehydrogenase (G6PDH) enzyme and free cotinine in the sample for a fixed amount of cotinine-specific antibody binding sites. The enzyme G6PDH activity is determined spectrophotometrically at 340 nm.