Carboxyhemoglobin, cotinine, and thiocyanate assay compared for distinguishing smokers from non-smokers.

We compared cotinine, carboxyhemoglobin, and thiocyanate concentrations in blood sampled from 187 cigarette smokers and 181 non-smokers. All three differed significantly between smokers and non-smokers. Cotinine performed best as a test for assessing smoking status, with a sensitivity of 98% as compared with 94% for carboxyhemoglobin and 80% for thiocyanate, all at a specificity of 95%. These differences were statistically significant. Results by none of these three methods correlated well with number of cigarettes smoked per day.