Estimation of level of serum cotinine: A simple, rapid and sensitive biomarker in cigarette smokers

Background: Cigarette smoking remains the leading preventable cause of morbidity and mortality worldwide. Cotinine, a metabolite of nicotine, serves as a reliable biomarker of tobacco exposure due to its longer half-life (18–20 h) compared to nicotine (2–3 h). Aims and Objective: The present study aimed to measure serum cotinine levels in cigarette smokers and examines their relationship with smoking duration and intensity, thereby validating smoking status. Materials and Methods: This case–control study was conducted at a tertiary care center in the Kumaon region of Northern India, including 284 healthy cigarette smokers (cases) aged 18–60 years and 284 age- and sex-matched non-smokers (controls). Detailed smoking histories were obtained, and participants were categorized into four groups based on cigarettes/day and duration: Very mild (Group I: 1–10/day, <5 years), mild (Group II: 11–20/day, <5 years), moderate (Group III: 11–20/day, 5–10 years), and heavy smokers (Group IV: 11–20/day, >10 years). Serum cotinine was quantified using high-pressure liquid chromatography. Results: Smokers were predominantly male, with a mean age of 41.68±11.52 years. Serum cotinine levels were significantly higher in smokers compared to non-smokers (P<0.05), with values increasing proportionally to smoking duration and intensity. Conclusion: This study demonstrates a strong positive correlation between serum cotinine levels and smoking behavior, supporting its utility as a biomarker for identifying and validating smoking status. Routine measurement of cotinine in serum or urine may aid in detecting both active and passive smokers, thereby enhancing tobacco control strategies.