Abstract
Objective: Cotinine is the preferred biomarker to validate levels of tobacco smoke exposure (TSE) in children. Compared to enzyme-linked immunosorbent assay methods (ELISA) for quantifying cotinine in saliva, the use of liquid chromatography tandem mass spectrometry (LC-MS/MS) has higher sensitivity and specificity to measure very low levels of TSE. We sought to compare LC-MS/MS and ELISA measures of cotinine in saliva samples from children overall and the associations of these measures with demographics and TSE patterns. Method: Participants were nonsmoking children (N = 218; age mean (SD) = 6.1 (5.1) years) presenting to a pediatric emergency department. Saliva samples were analyzed for cotinine using both LC-MS/MS and ELISA. Limit of quantitation (LOQ) for LC-MS/MS and ELISA was 0.1 ng/mL and 0.15 ng/mL, respectively. Results: Intraclass correlations (ICC) across methods = 0.884 and was consistent in sex and age subgroups. The geometric mean (GeoM) of LC-MS/MS = 4.1 (range: < LOQ to 382 ng/mL; 3% < LOQ) which was lower (p < 0.0001) than the ELISA GeoM = 5.7 (range: < LOQ to 364 ng/mL; 5% < LOQ). Similar associations of cotinine concentrations with age ( < −0.10, p < 0.0001), demographic characteristics (e.g., income), and number of cigarettes smoked by caregiver ( > 0.07, p < 0.0001) were found regardless of cotinine detection method; however, cotinine associations with sex and race/ethnicity were only found to be significant in models using LC-MS/MS-derived cotinine. Conclusions: Utilizing LC-MS/MS-based cotinine, associations of cotinine with sex and race/ethnicity of child were revealed that were not detectable using ELISA-based cotinine, demonstrating the benefits of utilizing the more sensitive LC-MS/MS assay for cotinine measurement when detecting low levels of TSE in children.
Highlights
Biochemical verification is the gold standard used to validate levels of tobacco smoke exposure (TSE) in children and the tobacco use status of smokers in clinical trials [1,2,3,4,5,6]
In order to ensure an accurate comparison of methods, only those samples with cotinine measured in both LC-MS/MS and enzyme-linked immunosorbent assay methods (ELISA) at T0 were included in the models (n = 203); samples taken at the six-week timepoint (n = 15) were excluded from these analyses
Ref-reference category; LCL-lower confidence level; UCL-upper confidence level. This is the first study conducted in a pediatric population to examine and compare salivary cotinine levels obtained with LC-MS/MS assays with levels obtained using ELISA
Summary
Biochemical verification is the gold standard used to validate levels of tobacco smoke exposure (TSE) in children and the tobacco use status of smokers in clinical trials [1,2,3,4,5,6]. It is recognized that child age and genetic variation in the frequency of CYP2A6 variant alleles among racial/ethnic groups [11,19] may result in differences in the rates and patterns of nicotine metabolism in children [1,20,21,22,23,24,25,26] These differences are pronounced in young children due to their increased exposure to tobacco smoke from active SHS or aged SHS (i.e., THS) due to close contact with caregivers who smoke, increased time spent indoors, increased contact with surfaces (e.g., floor, furniture), and high levels of hand-to-mouth behavior. LC-MS/MS was expected to provide more power, fewer values
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