Background <p>AECOPD is a leading cause of ICU admission and death in patients with COPD, yet readily accessible biomarkers for dynamic risk stratification remain scarce. The platelet-to-white blood cell ratio (PWR) is a promising inflammatory marker reflecting inflammatory burden and regenerative capacity. However, no studies have investigated PWR in AECOPD, and single-time-point measurements in critical illness are inherently limited by rapid physiological fluctuations. Whether longitudinal PWR trajectories outperform static measurements or conventional severity scores in AECOPD remains unknown. Accordingly, we investigated the association between dynamic PWR trajectories and all-cause mortality in this critically ill population.</p> Methods <p>Data were extracted from the Medical Information Mart for Intensive Care (MIMIC)-IV database. This retrospective cohort study enrolled critically ill patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD). Group-based trajectory modeling (GBTM) was used to identify distinct platelet-to-white blood cell ratio (PWR) trajectories; model selection was based on the Bayesian information criterion (BIC), average posterior probability (AvePP), odds of correct classification (OCC), and clinical interpretability. The primary outcome was 28-day all-cause mortality, with secondary outcomes including in-ICU, in-hospital, 90-day, and 365-day mortality. Multivariable Cox and logistic regression models were constructed to evaluate independent associations. Receiver operating characteristic (ROC) curves with the DeLong test were used to compare predictive performance. Subgroup and sensitivity analyses were performed to assess robustness, and restricted cubic spline (RCS) analysis was conducted to evaluate nonlinearity.</p> Results <p>Among 1,056 AECOPD patients, five distinct PWR trajectories were identified: Traj 1 (persistently low, <i>n</i> = 210), Traj 2 (low-to-moderate increasing, <i>n</i> = 333), Traj 3 (moderate-to-high increasing, <i>n</i> = 269), Traj 4 (moderate-to-low decreasing, <i>n</i> = 98), and Traj 5 (persistently high, <i>n</i> = 146). The primary findings demonstrated that compared with Trajectory 1, Trajectories 2, 3, and 5 were associated with significantly reduced risks of 28-day all-cause mortality, with adjusted hazard ratios (HRs) of 0.35 (95% confidence interval [CI]: 0.23–0.53), 0.45 (95% CI: 0.29–0.70), and 0.23 (95% CI: 0.12–0.46), respectively. In contrast, Trajectory 4 exhibited a comparable risk of 28-day mortality relative to Trajectory 1 (HR = 0.72, 95% CI: 0.43–1.20). Consistent patterns were observed for secondary outcomes, including the risks of in-hospital mortality, ICU mortality, 90-day mortality, and 365-day mortality. The PWR trajectory model (AUC = 0.661) outperformed single PWR (AUC = 0.596, <i>P</i> = 0.007) and was comparable to SOFA (AUC = 0.607, <i>P</i> = 0.051); their combination yielded the highest AUC (0.674, <i>P</i> = 0.002 vs. SOFA).</p> Conclusion <p>In critically ill patients with AECOPD, PWR trajectories are independently associated with short- and long-term mortality. PWR trajectories offer superior prognostic performance to single PWR, comparable performance to SOFA, and significant incremental value when combined.</p>