Association between creatinine-adjusted and unadjusted urine cotinine values in children and the motherʹs report of exposure to environmental tobacco smoke

Objective: To examine the association between parentsʹ report of their childʹs secondhand smoke exposure and various adjustments of cotinine concentrations in random urine samples. Methods: Urine cotinine and creatinine were measured in 109 six to 11-year-old children from predominantly upper middleclass families. Cotinine values were considered as: (a) unadjusted, (b) as a cotinine/creatinine ratio, (c) as adjusted based on a regression relationship between cotinine and creatinine, and (d) and (e) as a cotinine/creatinine ratio adjusted for age and sex. Results: Little overlap in cotinine values occurred between exposed and nonexposed children, and a dose-response relationship was noted between the parental report and the urine cotinine values (r = 0.67). A modest improvement occurred in the correlation when the cotinine/creatinine ratio was considered. Considering exposure to cigarette smoke outside the home as well as in the household only improved the correlation when the former exposure was heavy. A high degree of concordance exists between the parentsʹ report of exposure and the childʹs urine cotinine. Conclusions: The value of adjusting this biochemical parameter by various means may be a function of the particular sample being investigated, suggesting no one method is universally appropriate.