Evaluation of objective measures of smoking status--a prospective clinical study in a group of head and neck cancer patients treated with radiotherapy.

The present study was undertaken to evaluate objective measures of the smoking status of head and neck cancer patients during the course of radiotherapy. This was done by conducting a weekly structured interview, and measurement of carbon monoxide in expired air and of serum concentration of cotinine, the major metabolite of nicotine. These methods were tested prospectively in a series of 20 patients with head and neck cancer treated with radiotherapy. The results showed significant differences in the levels of end-expired carbon monoxide as well as serum cotinine among the different self-reported smoking groups. Combining the two objective measures and the interview data, the study revealed that up to 50% of self-reported non-smokers were in fact smoking actively. Measurement of end-expired carbon monoxide levels was found to be a precise indicator of smoking in the hours preceding measurement. Serum cotinine was a valuable measure of true smoking status. Assuming that this assay reflects the true smoking status, sensitivity, specificity and positive predictive value of self-reporting in this patient population was 79%, 80%, and 92%, respectively. In research aiming to investigate possible relations between smoking and radiotherapy, it is recommended that patients' smoking status be evaluated objectively as a supplement to self-reporting, at least in the head and neck cancer patients.