Association between prognostic nutritional index and 90-day readmission in patients with acute exacerbation of chronic obstructive pulmonary disease: a multicenter study.

BACKGROUND: Chronic obstructive pulmonary disease (COPD) is marked by chronic airway inflammation and obstructive ventilation dysfunction. The prognostic nutritional index (PNI), an indicator for evaluating nutritional and immune status with confirmed prognostic value in most diseases, has an unclear association with short-term acute re-exacerbation of COPD. This study thus investigated the correlation between PNI levels and 90-day acute re-exacerbation in COPD patients. METHODS: A cohort analysis was conducted on AECOPD patients, who were grouped by PNI tertiles. The primary outcome was 90-day readmission for acute re-exacerbation. Cox proportional hazards regression, Kaplan-Meier survival curves (Log-rank test), restricted cubic spline plots and subgroup analysis were applied for statistical assessment and conclusion verification. RESULTS: A total of 112 patients had acute re-exacerbation. Fully adjusted multivariate Cox regression identified PNI as a protective factor (HR = 0.914, 95% CI: 0.877 ~ 0.952, p < 0.001). Restricted cubic spline analysis confirmed a linear dose-response between PNI and 90-day readmission risk (overall p = 0.0002, non-linear p = 0.737), with an inflection point at PNI = 43.05. The cumulative incidence of readmission showed a significant difference across PNI tertile groups (Log-rank p = 0.003). Subgroup analysis revealed consistent protective trends across all subgroups, with no significant interaction effects detected (all interaction p > 0.05). CONCLUSION: PNI is an independent protective factor for short-term readmission in AECOPD patients, with a significant linear dose-response relationship and a clinical threshold of PNI = 43.05.