Which cut-off level of urine cotinine:creatinine ratio (CCR) should be used to determine passive smoking prevalence in children in community based studies?

1- 3 Exposure intensity of ETS among children shows a strong correlation with indoor parental and, especially, maternal smoking, the number of cigarettes smoked, the number and volume capacity of the rooms where cigarettes are smoked and individual metabolic diversities. 4 The use of cotinine, a major metabolite of nicotine, as a biological marker of smoke absorption has been suggested as an approach to strengthen the evidence of the relation between passive smoking and respiratory illness.