Objective To investigate the relationship between delayed diagnosis time (time from symptom onset to diagnosis) in patients with chronic obstructive pulmonary disease (COPD) and the burden of type 2 inflammation (defined as the persistent inflammatory status assessed by blood EOS counts, EOS%, and Fractional exhaled nitric oxide(FeNO) among other biomarkers).MethodsThis study was a single-center, observational study that included patients with COPD first diagnosis at the respiratory outpatient department of our hospital from June 2023 to December 2024. Asthma-COPD overlap (ACO) were identified according to the 2017 Spanish COPD guidelines. Clinical data were collected, including gender, age, delayed diagnosis time, acute exacerbations in the past year, pulmonary function tests, exhaled nitric oxide (FeNO), and type 2 inflammatory markers such as blood eosinophil counts (EOS). The correlation between the delayed diagnosis time and type 2 inflammation burden, as well as its influencing factors, were analyzed. Results A total of 195 patients were included, with 98 cases of COPD and 97 cases of ACO. The mean delayed diagnosis time was 18.0 (2.8, 37.5) months for the overall patients, 24.0 (1.0, 60.0) months for COPD, and 16.5 (3.0, 36.0) months for ACO, with no significant difference between the COPD and ACO groups (P>0.05). The median blood EOS counts, EOS%, andFeNO levels were 180 cells/μL, 1.9%, and 18 ppb in the COPD group, respectively, compared to 350 cells/μL, 4.7%, and 28 ppb in the ACO group, indicating higher type 2 inflammation levels in the ACO group (all P<0.001). A significant correlations were found between the disease course and the blood EOS counts and EOS% of the patients (respectively r=0.159, 0.152, all P<0.05).FeNO levels showed no significant correlation with delayed diagnosis time of COPD (P>0.05). Patients with a history of asthma and acute exacerbations in the past year had longer delayed diagnosis time and higher peripheral blood eosinophil counts (all P<0.05). Binary logistic regression analysis revealed that BMI and delayed diagnosis time were independent influencing factors for blood EOS counts (all P<0.05). ConclusionDelayed diagnosis of COPD was associated with aggravated type 2 inflammatory burden. Clinical practice should emphasize early recognition of COPD symptoms and implement prompt therapeutic interventions.