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Most nonsmokers by history had biomarker levels consistent with active or secondhand smoke exposure. A, Serum cotinine. B, Urine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL). The dots represent individual subjects. The y-axis is in log scale. The horizontal dashed line represents the cutoff between active and secondhand smoke exposure (serum cotinine = 3.1 ng/mL; urine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol = 64 pg/mg creatinine). Cr, creatinine.
