Objective: Participation in cardiac rehabilitation (CR) is associated with reduced morbidity and mortality. However, most programs rely on self-report measures when assessing the critical risk factor of smoking. This study examined smoking status using self-report versus objective measurement using expired carbon monoxide (CO) and compared patient characteristics by CO level. Method: Patients were screened for smoking status when entering CR by self-report and by objectively measured CO. Measures of aerobic fitness, educational attainment, depressive symptoms, and self-reported physical function were also collected. The discrepancy between smoking status based on self-report and objective measurement was examined and patient characteristics by CO measurement were compared. Results: Of the 853 patients screened, 62 self-reported current smoking and 112 had a CO of ≥4 ppm. Using a cut-off of ≥4 ppm encompassed almost all self-reported smokers (specificity: 98.5%) and identified 61 patients (not reporting current smoking) needing further screening. Further questioning yielded an additional 21 patients with combusted use (tobacco/cannabis), six nonsmoking patients with environmental CO exposure, and 34 where the reason for elevated CO was unknown. CO ≥4 ppm patients were younger (62.2 vs. 67.7, p < .01), had higher depression scores (5.6 vs. 3.7, Patient Health Questionairre-9, p < .01), had lower educational attainment (59.0% ≤high school vs. 31.3%, p < .01), had lower levels of fitness (after controlling for clinical characteristics, p < .01), and completed fewer CR sessions (18 vs. 22, p < .01). Conclusions: A substantial number of patients who are actively smoking may be misclassified by relying on patient report alone. CO monitoring provides a simple and objective method of systematically screening patients.

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