Measuring nicotine intake among highly-dependent adolescent smokers: comparability of saliva and plasma cotinine concentrations.

Cotinine is the most common biomarker used to assess nicotine exposure and abstinence. It can be measured in various matrices including saliva, plasma, and urine. Previous research with adults has shown high correlations between saliva and plasma cotinine concentrations. However, the research has not examined this relationship in adolescents. Additionally, variability in saliva flow and metabolism across gender, ethnicity, and age may impact the relationship between saliva and plasma cotinine concentration. Our aim was to examine the relationship between saliva and plasma cotinine concentration in a group of nicotine-dependent adolescent smokers. Additionally, we examined these correlations across gender, ethnicity and age. The sample consisted of 66 adolescent smokers (age 15.1+/-1.3, 63.6% girls, 66.7% European American, CPD 18.3+/-8.5, FTND 7.1+/-1.3). Saliva and plasma specimens were collected before the treatment phase of a nicotine replacement therapy trial and analyzed. The relationship between saliva and plasma cotinine concentration was analyzed using Pearson's correlation coefficients. We performed a secondary analysis using multiple regressions to compare correlations across race, gender and age. Results indicated a positive correlation between saliva cotinine and plasma cotinine concentration (r=0.84, p<0.001). Differences in correlations across age were significant (t=3.03, p<0.01). Differences across ethnicity approached significance (t=-1.93, p=0.058). Future research should seek to further validate saliva-to-plasma cotinine concentration ratios in adolescents as well as characterize saliva-to-plasma concentration differences and their underlying mechanisms.