Does breath carbon monoxide measure nicotine dependence?

The aim of the current study was the examination of exhaled breath carbon monoxide levels as a predictor for heaviness of smoking. In this regard, nicotine dependence was assessed among a representative sample of 1,870 Austrian male military conscripts in a cross-sectional setting. Participants completed the Heaviness of Smoking Index (a brief questionnaire for assessment of nicotine dependence), and their expired breath carbon monoxide levels were measured. The performance of carbon monoxide as a predictor of dependence levels was examined by means of Receiver-Operating-Characteristic Curve Analysis. Area Under the Curve, as well as sensitivity and specificity, were reported for each carbon monoxide cut-off level. The authors demonstrate that exhaled carbon monoxide levels serve as a satisfactory means to discriminate between smokers and non-smokers, yielding optimal discrimination at a cut-off level ≥ 5.5 parts per million (ppm), with a sensitivity of 95% and a specificity of 83%. However, the results indicate that carbon monoxide levels do not discriminate adequately between different levels of severity of nicotine dependence. The study demonstrates exhaled carbon monoxide as a useful marker of smoking status but not of nicotine dependence.