Carboxyhaemoglobin levels in smokers of filter and plain cigarettes.

Blood-carboxyhaemoglobin (COHb) levels were studied in 343 healthy male cigarette smokers aged 35-64. The mean COHb level was 30% higher in the 248 men who smoked unventilated filter cigarettes than in the 41 men who smoked plain cigarettes, after adjusting for the number of cigarettes smoked (P less than 0.001). This result was consistent with the carbon-monoxide (CO) yields of these cigarettes: on average, the unventilated filter cigarettes had yields 25% higher than the plain ones. The mean COHb level was 7% higher in the 54 men who smoked ventilated cigarettes than in men who smoked plain cigarettes. Although this difference was not statistically significant, it was in the opposite direction to the result which might have been expected on the basis of the CO yields of these cigarettes: on average the ventilated filter cigarettes had yields 21% lower than the plain ones. The medical implications of these results are uncertain. COHb levels of 3-4% or more can exacerbate angina pectoris and intermittent claudication, and it is, therefore, of concern that COHb levels are higher in smokers of filter cigarettes than in smokers of plain cigarettes. However, any assessment of risk associated with either type of cigarette should take account of the observation from other studies that filter cigarettes are associated with a lower mortality from lung cancer than are plain cigarettes.