Validation of self reported smoking by serum cotinine measurement in a community-based study.

STUDY OBJECTIVE The validity of self reported smoking in population surveys remains an important question. An associated question is what would be the value of measuring serum cotinine concentrations in such surveys to obtain validated smoking data. DESIGN Cross sectional analysis of data on self reported smoking and serum cotinine among a random population sample of 5846 persons aged 25 to 64 years, who participated in the FINRISK-92 survey. MAIN RESULTS Among self reported regular smokers, 97.2% of men and 94.9% of women had a cotinine concentration of 10 ng/ml or higher in serum. Of those participants who reported to have smoked at any time during their life but not during the previous month, 6.3% of men and 5.2% of women had a serum cotinine concentration of at least 10 ng/ml. Among never smokers 2.5% of men and 2.7% of women had detectable level of cotinine in their serum. The validity of self reporting was similar among subjects from different areas, ages, and socioeconomic groups. CONCLUSIONS In a sample of the general population in Finland the validity of self reported smoking is high, and most of the few self reported non-smokers who had cotinine in their serum had only low or moderate levels.