Background: Chronic obstructive pulmonary disease (COPD) is a systemic disease with several extrapulmonary comorbidities. However, studies to find out the relationship between COPD and renal impairment are scarce. This study aimed to assess the relationship of estimated glomerular filtration rate (eGFR) with chronic obstructive pulmonary disease assessment test (CAT) score, modified medical research council (mMRC) scale, 6-minute walking test (6MWT), and postbronchodilator forced expiratory volume (FEV₁) in COPD and to compare the reduction of eGFR in different GOLD stages. Materials and methods: A total of 240 stable COPD patients attending the outpatient department (OPD) were randomly selected between November 2019 and October 2020. Participants had spirometry, Global Initiative for Chronic Obstructive Lung Disease (GOLD) staging, CAT score, mMRC grading, and 6MWT. Serum creatinine was obtained and eGFR was calculated. The interpretation was made by comparing the results of the eGFR and GOLD stages with different parameters. Results: In patients with normal eGFR, the mean mMRC score was 2.00 ± 0.86, 6MWD was 324.98 ± 47.08 m, and CAT score was 14.23± 6.09. With reduced eGFR, the mean mMRC score was 2.32 ± 1.17, 6MWD was 278.30 ± 75.98 m, and CAT scoring was 19.38 ± 9.05. These were statistically significant (p = 0.0145, p < 0.0001, and p < 0.0001, respectively). A negative correlation was found between eGFR vs GOLD stages; the Pearson correlation coefficient (r) was −0.014. Conclusion: Reduction of eGFR was seen in stable COPD patients with higher GOLD stages. Patients with reduced eGFR had higher mMRC grade, increased CAT score, and reduced 6MWD. So, routine estimation of eGFR in patients of stable COPD is advocated to assess renal involvement.