Effect of collection time and reported cigarettes per day on exhaled carbon monoxide: a retrospective observational...

Research studies that include adults who smoke conventional combustible tobacco cigarettes (cigarettes) commonly use exhaled carbon monoxide (eCO) as a biomarker of cigarette usage. eCO is regularly used as an inclusion or exclusion criterion. Multiple studies have examined the time course of eCO levels after acute use of cigarettes. Published studies have verified the relationship between the reported number of cigarettes smoked per day (CPD) and eCO levels. One article suggested that collection time of day may induce variations in eCO elimination. Researchers can improve recruitment if there is confidence that collection time does not significantly affect eCO.

We analyzed data from eight separate studies conducted between 2019 and 2024 that collected eCO levels from adults who were not abstinent from smoking, after they reported their usual consumption patterns of cigarettes, to determine whether collection time or CPD had a significant effect on eCO levels. Data analyzed included eCO levels, collection times of eCO levels, and reported CPD smoked.

In the aggregate data, collection time did not result in significant changes in eCO levels (p = 0.87), as assessed throughout typical clinical hours (08:00 to 18:00). In contrast, and as expected, eCO levels were significantly impacted by CPD (p < 0.001).

This finding verifies that screening eCO levels may be obtained throughout the day while minimally impacting eCO levels, allowing for greater flexibility in scheduling individuals for participation in research studies which require evaluation of smoking status.