Misclassification of self-reported smoking in adult survivors of childhood cancer.

We investigated misclassification rates, sensitivity, and specificity of self-reported cigarette smoking through serum cotinine concentration (liquid chromatography tandem mass spectrometry) among 287 adult survivors of childhood cancer. Overall, 2.5-6.7% and 19.7-36.9% of the self-reported never and past smokers had cotinine levels indicative of active smoking. Sensitivity and specificity of self-reported smoking were 57.5-67.1% and 96.6-99.2%. Misclassification was associated with younger age (OR = 3.2; 95% CI = 1.4-7.4), male (OR = 2.1; 95% CI = 1.1-4.0), and past (OR = 2.7; 95% CI = 1.3-5.8) or current (OR = 2.6; 95% CI = 1.0-6.6) marijuana use. After adjusting for tobacco-related variables, current marijuana use remained a significant risk for misclassification. Clinicians/researchers should consider bio-verification to measure smoking status among survivors.