Urine cotinine versus self-reported smoking and the risk of chronic kidney disease

Background and hypothesis Evidence on the role of smoking in the development of chronic kidney disease (CKD) has mostly relied on self-reported smoking status. We aimed to compare the associations of smoking status as assessed by self-reports and urine cotinine with CKD risk. Methods Using the PREVEND prospective study, smoking status was assessed at baseline using self-reports and urine cotinine in 4333 participants (mean age, 52 years) without a history of CKD at baseline. Participants were classified as never, former, light current, and heavy current smokers according to self-reports and comparable cutoffs for urine cotinine. Hazard ratios (HRs) with 95% confidence intervals (CIs) were estimated for CKD. Results The percentages of self-reported and cotinine-assessed current smokers were 27.5% and 24.0%, respectively. During a median follow-up of 7.0 years, 593 cases of CKD were recorded. In analyses adjusted for established risk factors, the HRs (95% CI) of CKD for self-reported former, light current, and heavy current smokers compared with never smokers were 1.17 (0.95–1.44), 1.48 (1.10–2.00), and 1.48 (1.14–1.93), respectively. On further adjustment for urinary albumin excretion (UAE), the HRs (95% CI) were 1.07 (0.87–1.32), 1.26 (0.93–1.70), and 1.20 (0.93–1.57), respectively. For urine cotinine-assessed smoking status, the corresponding HRs (95% CI) were 0.81 (0.52–1.25), 1.17 (0.92–1.49), and 1.32 (1.02–1.71), respectively, in analyses adjusted for established risk factors plus UAE. Conclusion Self-reported current smoking is associated with increased CKD risk, but dependent on UAE. The association between urine cotinine-assessed current smoking and increased CKD risk is independent of UAE. Urine cotinine-assessed smoking status may be a more reliable risk indicator for CKD incidence than self-reported smoking status.