The Impact of Lung Function Case-Finding Tests on Smoking Behaviour: A Nested Randomised Trial Within a Case-Finding Cohort.

Rationale, aims, and objectives Increasing awareness of people's lung health through the use of lung function tests or symptom-based questionnaires is a potential method to aid smoking cessation. We investigated the impact of case-finding lung function tests for chronic obstructive pulmonary disease on smoking behaviour. Methods Our trial used a novel waiting list randomised controlled trial design, nested within a case-finding cohort study. The cohort comprised current smokers aged 35 years or more, from general practices in Yorkshire and Humberside, who were randomised to receive lung function tests (spirometry, microspirometry, peak flow meter measurement, and a WheezoMeter) and case-finding questionnaires either immediately ("tests now") or later ("waiting list" control). Outcome measures included self-reported smoking cessation and number of cigarettes smoked at follow-up (at 2, 3, or 6 months after randomisation, depending on study site), with 409 participants included in the primary analysis. Results Six hundred seventy-four participants were randomised using stratified block randomisation to the 2 groups (340 to "tests now" and 334 to "waiting list"), with 409 included in the primary analysis (194 in "tests now" and 215 in "waiting list" groups). Smoking cessation at follow-up was very similar across groups (8.8% in the "tests now" group, compared with 9.2% in the "waiting list" group). Completing case-finding lung function tests did not significantly impact smoking cessation (OR 1.00, 95% CI, 0.57-1.77, adjusting for age, sex, baseline number of cigarettes smoked, and study site). A sensitivity analysis, assuming that participants with missing data were still smoking, gave similar results (OR 0.86, 95% CI, 0.47-1.56). Analysis of the number of cigarettes smoked at follow-up using negative binomial regression adjusting for the same factors above gave an incidence rate ratio of 0.95 (95% CI, 0.88-1.03). Conclusions There is no evidence from this trial of an effect of lung function tests on smoking cessation among a population of smokers aged 35 years or over. Indeed, when assuming that those with missing data were smokers, a slightly lower odds of smoking cessation was observed in the "test now" group compared with the "waiting list" group.