A Cochrane review included 15 studies with a total of 6 321 subjects. E.g., measurement of exhaled carbon monoxide (CO), lung function, or genetic susceptibility to lung cancer were used as feedback on the biomedical or potential future effects of smoking.
Two pairs of trials had sufficiently similar recruitment, setting and interventions to calculate a pooled effect; there was no evidence that CO measurement in primary care (RR 1.06, 95% CI 0.85 to 1.32) or spirometry in primary care (RR 1.18, 95% CI 0.77 to 1.81) increased cessation rates. The other 11 trials were not pooled. One good quality study (n=561) in primary care detected a significant benefit of lung age feedback after spirometry (RR 2.12, 95% CI 1.24 to 3.62). One study (n=155) that used ultrasonography of carotid and femoral arteries and photographs of plaques detected a benefit (RR 2.77, 95% CI 1.04 to 7.41) but enrolled a population of light smokers. 9 trials failed to detect evidence of a significant effect. One of these tested CO feedback alone and CO + genetic susceptibility as two different intervention. 4 others used a combination of CO and spirometry feedback in different settings.
Comment: The quality of evidence was downgraded by study quality (inadequate or unclear allocation concealment) and by inconsistency (heterogeneity in interventions and populations).