SINGLE BREATH DIFFUSING-CAPACITY IN A REPRESENTATIVE SAMPLE OF THE POPULATION OF MICHIGAN, A LARGE INDUSTRIAL-STATE - PREDICTED VALUES, LOWER LIMITS OF NORMAL, AND FREQUENCIES OF ABNORMALITY BY SMOKING HISTORY

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Abstract
Many predictive equations for the single breath CO diffusing capacity (DLCOsb) are based on small, selected populations and do not account for the effect of cigarette smoking. This test was performed on 582 white adults who were part of a stratified random sample of the population of Michigan, [USA], a large industrial state. Data on 511 subjects who had full clinical information and normal Hb concentration provided prediction equations and lower 95% limits for current cigarette smokers, ex-smokers, and nonsmokers. These are the 1st equations, obtained by sampling the general population of an entire state. Significant differences in the level of DLCOsb were found between smoking categories. To obtain information on the frequency with which DLCOsb would be reported as abnormal in a general population, the test results for all 582 subjects were compared with reference values. Use of equations that do not take smoking into account classified 30% of the male and 28% of the female smokers as abnormal, whereas, only 5% of male and 9% of female smokers were classified as abnormal using the smoking-specific equations. The Michigan equations are of value both in clinical medicine and occupational surveys. For both applications, it is essential to have reference values that are derived from a large number of subjects who are representative of the general population and for whom smoking habits are accounted.