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 continine of pregnant women participating in a smoking cessation trial, determine the relationship of the number of cigarettes smoked per day and saliva continine, and examine whether misclassification was due to an inappropriate saliva continine cutoff point. METHODS: End of pregnancy self-reports of smoking status and saliva continine 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 continine 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 continine 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 continine to distinguish smoking status in this study.