The validity of self-reported smoking status on day of surgery in a mixed elective surgery population

Rates of misrepresenting smoking status on day of surgery varies with the clinical context. In perioperative smoking cessation trials, participants in the intervention group might be more likely to provide untruthful data about quitting when they have received substantial quit support but continued to smoke. The objective of this study was to determine misrepresentation rates of smoking status on day of surgery in mixed elective surgical populations, comparing groups offered or not offered additional cessation support. We undertook a post hoc analysis of data from three published randomised trials at a Melbourne public hospital that incorporated interventions during the wait-list period aimed at increasing smoking cessation. Participants were smokers (<i>n</i> = 1413) who were randomised to minimal cessation help at wait-listing (control group) or significant assistance, for example, mailed nicotine replacement (intervention group). Quit by day of surgery claims were verified by exhaled carbon monoxide (true cessation <8 parts per million). Verified cessation (>24 h) before surgery occurred in 161/1413 (11.4%) while 44/1413 (3.1%) misrepresented quitting. Continued smoking was in 1208/1413 (85.5%). Misrepresentations were higher in the intervention/offer of help groups (4.1%) than control groups (1.7%) (odds ratio (OR) 2.46, 95% confidence interval (CI) 1.17 to 5.63, <i>P</i> = 0.012). Offering cessation help increased quitting odds by 77%, (OR 1.77, 95% CI 1.24 to 2.52, <i>P</i> = 0.002). In contrast to other studies, we found group allocation in cessation trial settings had a significant effect on misrepresentation risk. The implication of this is that biochemical verification of quit status is essential in trial contexts for accurate data collection and to prevent misclassification bias.