Measuring the exposure of infants to tobacco smoke. Nicotine and cotinine in urine and saliva.

The effect of parental smoking on the well-being of infants and children is an important public health concern. It is necessary, however, to validate the existence of such exposure objectively before an evaluation of the effects of parental smoking behavior on the child's health can be made. We measured the concentration of nicotine and its major metabolite, cotinine, in the saliva and urine of 32 infants with household exposure to tobacco smoke, and 19 unexposed infants. The concentrations were significantly higher in the exposed group than in the unexposed group, with the best indicator of chronic exposure being the urinary cotinine:creatinine ratio; median in the exposed group, 351 ng per milligram (225.3 nmol per millimole); median in the unexposed group, 4 ng per milligram (2.6 nmol per millimole) (P less than 0.0001). There was a direct relation between cotinine excretion by the infants and the self-reported smoking behavior of the mothers during the previous 24 hours (r = 0.67, P = 0.0001). Our results indicate that infants who were exposed to tobacco smoke absorbed its constituents and that urinary excretion of cotinine is a reliable measure of such exposure in infants.