Inflammation-Based Hematologic Indices as Prognostic Markers in Pulmonary Arterial and Chronic Thromboembolic Pulmonary Hypertension: A Hypothesis-Generating Registry Study

Pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH) are characterized by high morbidity and mortality. We retrospectively analyzed 468 hospital admissions from 80 patients to evaluate the prognostic value of inflammation-based hematologic indices, including the neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), neutrophil-percentage-to-albumin ratio (NPAR), lymphocyte-to-monocyte ratio (LMR), and systemic immune-inflammation index (SII). All biomarker-outcome associations were specified a priori as exploratory in this hypothesis-generating design. In PAH, both NPAR and SII were associated with in-hospital mortality (odds ratio [OR] 1.129, 95% confidence interval [CI] 1.011-1.261, <i>p</i> = 0.031; OR 1.001, 95% CI 1.000-1.002, <i>p</i> = 0.002), post-discharge mortality (NPAR OR 1.181, 95% CI 1.062-1.313, <i>p</i> = 0.002), and poorer overall survival (log-rank <i>p</i> = 0.002 and <i>p</i> = 0.012, respectively). Higher LMR was associated with reduced in-hospital mortality (OR 0.291, 95% CI 0.108-0.790, <i>p</i> = 0.015), while NLR predicted increased in-hospital mortality. In CTEPH, NLR and LMR were the strongest predictors, correlating with worse survival (log-rank <i>p</i> = 0.007 and <i>p</i> = 0.044) and higher post-discharge mortality (NLR OR 1.289, 95% CI 1.029-1.615, <i>p</i> = 0.027). Receiver operating characteristic (ROC) analysis suggests the potential value of SII in PAH and the promising performance of NPAR in CTEPH. Inflammation-based hematologic indices, particularly NPAR, SII, and NLR, may provide valuable prognostic information and may serve as practical, non-invasive tools for predicting hospitalization duration and mortality in PAH and CTEPH.