ABC of Diabetes

12-9; No=7; (b) 95 fimol/l; 14 6; No=8; (c) 75 pmol/l; 15-3; No= 6. (Prior to two further samples from (c) the subject had reduced his cigarette consumption (thiocyanate=48 pmol/l) and stopped smoking (thiocyanate =12 tmol/l)). When estimating the effective exposure to tobacco, self-reported cigarette consumption has major limitations. Quite apart from inaccurate and biased reporting of numbers, it does not allow for the type or brand of cigarette used and the smoker's manipulation of his smoking in terms of puffing and inhalation. Biochemical markers are more objective and provide estimates of actual intake of smoke products. By studying the relation between carboxyhaemoglobin, thiocyanate, and cigarette consumption we have shown that the number of cigarettes and the manner of smoking contribute almost equally to the variation in the blood concentrations of these substances. Therefore consumption alone is clearly not a sufficient measure of dose. This view is further supported by the finding that in those groups smoking more than 25 cigarettes a day an increase in consumption did not produce a proportionate rise either in mean carboxyhaemoglobin or in mean thiocyanate concentrations and there was a wide range of concentrations within each smoking group (see figs 1 and 2 in our original paper). Furthermore the correlations we obtained between the variables were similar to those reported for an American study,6 which confirms the repeatability of these findings in a different population. We do not suggest that biochemical estimations supplant questionnaires on smoking history and habits in epidemiological studies but agree that information from both sources could be complementary. While more research is needed into quantifying exposure to tobacco smoke and the accuracy of biochemical measures in assessing this, we believe that our statistical analysis and the conclusions we draw from our observations are valid.