Objective: The study aims to investigate the incidence of early stage kidney disease in outpatients with acute carbon monoxide poisoning (CMP) and to assess whether the Chronic Kidney Disease Epidemiology Collaboration formula (CKD-EPI)values of these patients had any impact on the time taken for their discharge. Materials and Methods: This retrospective case–control study consisted of a total of 94 patients (47 patients with carbonmonoxide poisoning induced by exposure to incompletely burned coal, and 47 age-and sex-matched controls). Patient detailsincluding age, CKD-EPI value, hemoglobin, carboxyhemoglobin (COHb), lactate, pH, SaO2, pO2 pCO2, BE, HCO3, glucose,AST, ALT, amylase, ALP, BUN, creatinine, Na, K, Cl, CK, CK-MB, troponin, uric acid levels and duration of follow-upwere recorded. The post-hoc power analysis was calculated using G*Power 3.1.9.2 based on the difference between the twomeans by Wilcoxon–Mann–Whitney test. A Kaplan–Meier survival curve was plotted and test of equality of survival distributions for the different levels of CKD-EPI was compared. Results: The mean age and mean COHb values of the study group were 37.24±12.91 and 21.45±9.89, respectively.The CKD-EPI values were lower in patients belonging to the CMP group (101.39±19.53) compared to the control group(114.92±14.81) (p=0.017), 92% power level, d=0.781, 95% confidence intervals (CI) on the difference between means(-23.01/-4.04). The duration of follow-up of patients with CMP was 29.04±9.7 hours. There was a significant relationshipbetween the follow-up duration of patients with CMP in the emergency department and their CKD-EPI levels (Log-rank/ Mantel–Cox, p<0.001). Conclusion: CKD-EPI-values are reduced as a result of impaired renal function in outpatients with CMP in the early stages.Thus, long-term nephrology follow-up should be performed in outpatients diagnosed with CMP. Further investigations maybe required to rule out possible chronic kidney disease (CKD) associated with impaired renal function induced by acute CMP