Carboxyhaemoglobin (COHb) levels were studied in 11 249 men. The distribution among the 2613 men who smoked cigarettes was well separated from that in 6641 non-smokers (including ex-smokers The level of carboxyhaemoglobin (COHb) in the blood has been shown to be a useful marker of tobacco smoke absorption, 1-6 and for this reason there are epidemiological and clinical reasons for performing COHb measurements. The precise distributions of COHb levels in smokers and nonsmokers, and the extent to which they overlap, are not well known. We therefore investigated this in over 11 000 men. We also investigated the measurement of carbon monoxide (CO) in alveolar breath using a portable analyser, as an indirect measure of the COHb level which avoids the inconvenience of taking blood samples. Methods

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, A. (1978). Thorax, 33,[201][202][203][204][205][206]. Carboxyhaemoglobin levels and inhaling habits in cigarette smokers. In 520 men who currently smoked only cigarettes, carboxyhaemoglobin (COHb) levels were measured as a method of estimating the extent to which cigarette smoke was inhaled and the results were compared with the smokers' own assessment of their inhaling habits. The mean COHb level after standardising for the number of cigarettes smoked before the blood test on the day of the test was 4'0% in self-described non-inhalers. This was much higher than the mean level of 0'7% in 1891 similar non-smokers, but not very different from the standardised mean levels of 5-2%, 5-3%, and 566% in men who said they inhaled slightly, moderately, or deeply, respectively. The increasing trend in the COHb levels of men in the four self-described inhaling categories (nil to deep) was small but statistically highly significant. The data from this study may help to explain some of the anomalous epidemiological results regarding the relationship between self-described inhaling habits and the development of diseases associated with smoking, such as coronary heart disease and lung cancer.

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