Abstract
In this cross-sectional population study we report on the distribution of carboxyhaemoglobin concentrations in the morning, before smoking, in an urban population of 1037 men born in 1931. The median concentration was the same in non-smokers as in ex-smokers: 0.5%. It increased with increasing daily tobacco consumption. But when carboxyhaemoglobin concentrations are measured in reasonably well-standardised circumstances there are large variations between individuals, even in those who smoke equal amounts of tobacco a day. This makes it difficult to predict the concentration in the individual smoker when only his daily tobacco consumption is known. Measurements of carboxyhaemoglobin concentration should be a valuable complement to smoking history to identify the smoker at high risk of cardiovascular disease, to provide an extra argument to make the patient give up the habit, and to reinforce the efforts of those who try to do so.