Concentrations of serum cotinine across stages of glomerular function among US adult smokers and nonsmokers

Data from National Health and Nutrition Examination Survey for 1999–2016 were used to investigate variabilities in serum cotinine levels for US adult smokers (N = 8951) and nonsmokers (N = 28,205) aged ≥ 20 years across the stages of glomerular function (GF). Those with serum cotinine levels < 3.3 ng/mL and did not report using any tobacco products during the last 5 days were classified as nonsmokers. Those with serum cotinine levels ≥ 3.3 ng/mL and reported using cigarettes, cigars, pipes, and/or water pipes with or without using e-cigarettes and/or smokeless tobacco products during the last 5 days were classified as nonsmokers. Those who had eGFR > 90 mL/min/1.73 m² were classified to be in GF stage 1 or GF-1, those with 60 ≤ eGFR ≤ 90 mL/min/1.73 m² were classified to be in GF-2, those with 45 ≤ eGFR < 60 mL/min/1.73 m² were classified to be in GF-3A, and those with 15 ≤ eGFR <45 mL/min/1.73 m² were classified to be in GF-3B/4. Among nonsmokers, except for females and non-Hispanic blacks, adjusted levels of serum cotinine (AGM) decreased relatively sharply from GF-1 to GF-2, stayed relatively stable at GF-2 and GF-3A, and then rose moderately to GF-3B/4. For example, for non-Hispanic whites, AGMs were 0.042, 0.033, 0.031, and 0.037 ng/mL at GF-1, GF-2, GF-3A, and GF-3B/4 respectively. Among smokers, except for females and non-Hispanic blacks, AGMs increased relatively sharply from GF-1 to GF-2 and then decreased from GF-2 to GF-3/4. For example, for males, AGMs were 151.9, 192.0, and 162.9 ng/mL at GF-1, GF-2, and GF-3/4 respectively. AGMs for male smokers were lower than for female smokers at GF-3/4 (162.9 vs. 197.2 ng/mL, p < 0.01). The order of AGMs by race/ethnicity was non-Hispanic blacks > non-Hispanic whites > Hispanics and others at every GF stage. AGMs at GF-3/4 were higher than AGMs at GF-1 for smokers.