Alveolar Carbon Monoxide and Carboxyhaemoglobin

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 distribution for 2005 cigar and pipe smokers was intermediate, though some of the highest COHb levels occurred in cigar smokers. Using a COHb cut-off level of 2%, 81% of cigarette smokers, 35% of cigar and pipe smokers, and 10% of non-smokers had raised COHb levels. In a subsidiary experiment alveolar air samples were collected from 162 smokers and 25 non-smokers using a simple breath sampling technique. Carbon monoxide concentrations in alveolar breath were highly correlated with COHb levels (r=0-97) indicating that COHb levels can be estimated reliably by measuring the concentration of carbon monoxide in breath. Alveolar carbon monoxide measurement is thus a simple method of estimating whether a person is likely to be a smoker. 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.