Cotinine: The major metabolite (breakdown product) of nicotine. Exposure to nicotine can be measured by analyzing the cotinine level in the blood, saliva, or urine. Since nicotine is highly specific to tobacco smoke, serum cotinine levels track exposure to tobacco smoke and its toxic constituents.
Cotinine assays provide an objective quantitative measure that is more reliable than smoking histories or counting the number of cigarettes smoked per day. Cotinine also permits the measurement of exposure to second-hand smoke (passive smoking).
Cotinine is an anagram of nicotine. (The 8 letters in the word "nicotine" were rearranged to coin the word "cotinine.")