Expired air carbon monoxide and serum thiocyanate as objective measures of cigarette exposure

Expired air carbon monoxide (CO) and serum thiocyanate (SCN) were used to assess exposure to cigarettes in 139 middle-aged men. Subjects who reported smoking cigarettes generally had CO levels exceeding 8ppm and SCN levels exceeding 100μmol/L; non-smokers had lower levels. For both tests the mean concentration among men smoking more than 1 pack daily was 3 times that of non-smokers. There is a high correlation between the 2 tests (r=.571 for smokers), an association that was largely independent of the smaller correlations between either test and reported smoking frequency (r=.476 for CO; r=.479 for SCN). The ability to distinguish between individuals who reported 'typical' smoking habits and non-smokers was best when the CO and SCN analyses were used together to take advantage of their separate sources of variance; it was 99% when the 2 tests were mutually concordant (91% of cases). The CO and SCN measurements allowed 16 individuals who reported light smoking habits to be categorized into high and low presumptive tobacco exposure groups. The 2 tests are inexpensive and suitable for use in epidemiologic and health care delivery programs.