Biomarker-questionnaire discordance in secondhand smoke exposure among Korean children: A secondary analysis of the Korean National Environmental Health Survey, 2016-2017 and 2019-2020.

INTRODUCTION: Questionnaire-based assessment of secondhand smoke (SHS) exposure may not fully capture children's internal nicotine burden. We assessed concordance between parent-reported SHS exposure and urinary cotinine classifications and examined correlates of discordance by developmental stage and survey cycle. METHODS: This secondary analysis included children aged 3-11years with urine specimens and parent-completed questionnaire data from two independent cross-sectional samples in the Korean National Environmental Health Survey (KoNEHS 2016-2017 and 2019-2020; N=2619). Pooled analyses were unweighted; cycle-specific weighting was examined in sensitivity analyses. Concordance between parent-reported SHS exposure (≥1 time/week) and urinary cotinine-based classifications at three prespecified thresholds [at or above the limit of detection (LOD), ≥3 ng/mL, and ≥5 ng/mL] was evaluated using sensitivity, specificity, Cohen's κ, and McNemar's test. Correlates of questionnaire-negative/biomarker-positive discordance were examined using multivariable logistic regression. RESULTS: Concordance was negligible across thresholds and age groups (κ range: -0.02-0.01; McNemar p<0.001 for most strata). Sensitivity ranged from 7.1% to 16.1%, and at least 83.9% of biomarker-positive children were questionnaire-negative. Parent-reported SHS exposure was lower in Cycle 4 among children aged 3-5 and 6-8 years, whereas urinary cotinine concentrations were higher across all age groups. Among children aged 3-5 and 6-8 years without parent-reported SHS exposure, cotinine concentrations were higher in those with at least one current parental smoker than in those with no current parental smoker. At ≥LOD, questionnaire-negative/biomarker-positive discordance was associated with younger age (3-5 vs 9-11 years: adjusted odds ratio, AOR=1.64; 95% CI: 1.20-2.24) and with Cycle 4 (vs Cycle 3: AOR=2.09; 95% CI: 1.59-2.75). CONCLUSIONS: Parent-reported SHS exposure and urinary cotinine classifications showed marked discordance. These measures captured related but non-interchangeable information; urinary cotinine may complement questionnaires when characterizing children's internal nicotine burden.