TABLE 2.

Mean Difference (95% CI) of eGFR by Serum Cotinine Concentrations in US Adolescents 12 to 17 Years of Age

Exposure Categorya (Cotinine Levels)	N	Model 1	Model 2	Model 3
Unexposed <0.05 ng/mL	2897	0.0 (reference)	0.0 (reference)	0.0 (reference)
Secondhand smoke
0.05–0.10 ng/mL	1182	−1.7 (−3.5 to 0.1)	−1.0 (−2.7 to 0.7)	−0.4 (−1.9 to 1.2)
0.10–0.54	1326	−2.8 (−4.9 to −0.6)	−2.3 (−4.2 to −0.4)	−0.9 (−2.7 to 0.9)
0.55–10	1184	−3.5 (−5.8 to −1.3)	−3.7 (−5.7 to −1.6)	−2.2 (−4.0 to −0.4)
P trendb		<.001	<.001	.03
Active smoking
0.05–12 ng/mL	335	−4.3 (−7.1 to −1.6)	0.09 (−2.4 to 2.6)	0.2 (−2.2 to 2.6)
12–103	319	−9.8 (−12 to −7.7)	−2.5 (−4.5 to −0.5)	−1.9 (−3.8 to −0.0)
≥104	273	−11.7 (−14.0 to −9.4)	−3.5 (−5.8 to −1.3)	−2.6 (−4.6 to −0.6)
P trendb		<.001	<.001	<.01
Per IQR increase in serum cotinine	7516	−3.9 (−4.6 to −3.2)	−1.38 (−2.1 to −0.6)	−1.1 (−1.8 to −0.3)

Model 1, crude; model 2, adjusted for age and gender; model 3, further adjusted for BMI, parental educational level, race/ethnicity, and NHANES year.

^aSecondhand smoke and active smoking categories were divided into tertiles according to serum cotinine concentrations within each category.

^bP values for trend were obtained separately for participants exposed to secondhand smoke and for active smoking.