Comparison of Total Antioxidant Capacity in COPD, Asthma, and Asthma–COPD Overlap Patients

<i>Background and Objectives:</i> Asthma, COPD, and asthma-COPD overlap are obstructive lung diseases with inflammation at their core. Oxidative stress and impaired antioxidant balance play a significant role in etiopathogenesis. This study aimed to determine whether there are differences in total antioxidant capacity (TAC) between asthma, COPD, and asthma-COPD overlap. <i>Materials and Methods:</i> A total of 76 patients participated in this prospective cross-sectional study. TAC levels in fasting venous blood samples were measured using a biochemistry analyzer and the total antioxidant activity method (Architect C1600, Abbott Laboratories, IL, USA). <i>Results</i>: TAC levels were lower in COPD patients compared to asthma and ACO patients (<i>p</i> = 0.049 and 0.026, respectively). TAC levels were lower in current and former smokers compared to never smokers (<i>p</i> = 0.033). There was no significant correlation between TAC level and eosinophil count (<i>p</i> = 0.597) and FEV1 and FEV1/FVC (<i>p</i> = 0.372 and <i>p</i> = 0.189). <i>Conclusions</i>: Our results suggest that TAC levels may serve as a marker to differentiate COPD from asthma or ACO.