Competitive interaction between smoking and chronic obstructive pulmonary disease for explaining renal function reduction in hypertensive patients.

Chronic kidney disease is a risk factor for cardiovascular events. Smoking and chronic obstructive pulmonary disease (COPD) are risk factors for renal impairment. The aim of this study was to test the combined effect of smoking and COPD on renal function decline in hypertensives. We enrolled 1728 hypertensives stratified by smoking status and presence/absence of COPD. To test the mutual effect modification by both smoking and COPD and e-GFR, we performed crude and adjusted linear regression analyses, these latter taking into account potential confounders. Smokers displayed significantly lower e-GFR values than non-smokers (90 ± 24 vs. 121 ± 35 ml/min/1.73 m2); this difference was confirmed when comparing e-GFR values between patients with/without COPD (81 ± 17 vs. 109 ± 32 ml/min/1.73 m2). Smoking and COPD were directly and significantly interrelated (Cramer's V coefficient = 0.200; P =  < 0.001). At interaction analyses, smoking significantly modified the effect of COPD on e-GFR and COPD significantly modified the effect of smoking on e-GFR, indicating a competitive interaction between smoking and COPD in the appearance of renal damage. e-GFR was 35 ml/min/1.73 m2 lower in patients with COPD than in those without; this reduction was of higher magnitude than that found between COPD and COPD-free patients among smokers (19 ml/min/1.73 m2). Smoking and COPD competitively interact in the appearance of renal function decline. These results suggest to screen for kidney damageboth smokers and COPD patients, especially those with both conditions.