Variation of serum and urine cotinine in passive and active smokers and applicability in preconceptional smoking cessation counseling.

This study assessed the applicability of serum and urine cotinine as a biochemical marker of self-reported smoking habits for use in a preconceptional smoking cessation program. The variation of serum and urine cotinine over the course of the day was investigated in a sample of 21 smokers and 8 passive smokers who reported their smoking habits and exposure to smoke daily in a questionnaire for 10 consecutive days. Blood and urine samples were collected on two sampling days, 1 week apart. Both serum and urine cotinine assay could distinguish between passive and active smokers, but not between higher categories of smokers (10-19 and > or = 20 cigarettes per day) due to significant intersubject overlap. In serum, no significant differences were found between morning and afternoon cotinine concentrations on either day, in contrast to urine cotinine (with lower excretions observed in the morning). An overall coefficient of variation of 22% was observed for both specimens in smokers. Because serum cotinine is subject to lower variability over the course of the day, it is more practical for use in a clinical setting where appointments are scheduled throughout the day in order to confirm smoking status.