Quality of Measurement of Smoking Status by Self-Report and Saliva Cotinine Among Pregnant Women

Objective. The objectives of this paper were to determine the rate of misclassification of smoking and nonsmoking status by self-reports and saliva cotinine of pregnant women participating in a smoking cessation trial, determine the relationship of the number of cigarettes smoked per day and saliva cotinine, and examine whether misclassification was due to an inappropriate saliva cotinine cutoff point. Methods. End of pregnancy self-reports of smoking status and saliva cotinine were used to calculate misclassification rates. Results. The findings revealed that 61 of 441 self-reported smokers had biochemical values inconsistent with smoking status for a smoking misclassification rate of 13.8%. The results also revealed that 28 of 107 self-reported quitters had cotinine values consistent with smoking status for a nonsmoking misclassification rate of 26.2%. Receiver Operating Characteristic (ROC) curves were then plotted to determine whether misclassification resulted from an inappropriate cutoff point. The cotinine cutoff point that maximized sensitivity and specificity for all women was 24 ng/ml. Racial ROC comparisons indicated a higher cutoff point for blacks than whites. Use of any of the ROC indicated cutoff points would not change the misclassification rates. Conclusions. These findings suggest that underreporting of smoking status during pregnancy is high and that social desirability of nonsmoking status may have contributed to the lack of precision in saliva cotinine to distinguish smoking status in this study.