Association of Air Flow Limitation Severity with eGFR in Stable COPD Patients: A Cross-Sectional Study

Chronic obstructive pulmonary disease (COPD) is primarily a lung disease, but its consequences also affect other vital organs. Forced expiratory volume in one second (FEV₁), a basic spirometry finding along with others (Predicted FEV₁% and FVC), is essential for COPD diagnosis and severity analysis. Renal functional evaluation is essential, in addition to other systemic evaluations. Its evaluation is important because drugs used for the treatment of COPD are mostly excreted through the kidneys, which may cause its impairment. The estimated GFR (eGFR) by the modification of the diet in renal disease (MDRD) study group equation can approximate the actual GFR. This study aimed to elicit the association between airflow limitation severity and eGFR in stable COPD patients. This cross-sectional observational study included 95 patients with stable COPD who presented at the NIDCH between June 2018 and June 2019. The mean spirometry indices were compared with the eGFR-based groups (eGFR ≥60 mL/min/1.73 m² and eGFR <60 mL/min/1.73 m²). Correlation test was done to elicit the association of FEV₁ with eGFR. In addition, the prediction capability of eGFR along with other clinically relevant effector variables for FEV₁ was analyzed. FEV₁ was strongly correlated with eGFR (r=0.754, p<0.001). Predicted FEV₁% and FVC had moderate correlations with eGFR (r=0.646, p<0.001 and r=0.691, p<0.001, respectively), whereas FEV₁/FVC had weak correlations with eGFR (r=0.440, p<0.001). eGFR showed good prediction capability (β=-0.176, p<0.001) among other clinically relevant effector variables (age, sex, smoking, exacerbation history, mMRC grade, CAT score and BMI). All spirometry indices (FEV₁, PFEV₁%, FVC and FEV₁/FVC) were correlated with eGFR. FEV₁ was strongly correlated (positively) with eGFR and showed linear relation. Furthermore, eGFR had a good predictive capability for FEV₁. FEV₁ in stable COPD patients can be used as a predictor of renal function (eGFR), enabling early detection of renal functional impairment. Based on this, further evaluation, preventive measures or modifications in treatment strategy could be adopted accordingly.