In 968 hospitalized pericarditis patients drawn from two independent databases — a Hong Kong CDARS cohort (n=504) and MIMIC-IV (n=464) — elevated baseline neutrophil-to-lymphocyte ratio (NLR) and systemic immune-inflammation index (SII) were independently associated with increased all-cause mortality. Patients in the highest NLR tertile faced a 60% greater adjusted mortality hazard (HR 1.60) versus the lowest tertile; SII showed a comparable signal (HR 1.55). Crucially, both associations replicated directionally across 30-day, 90-day, and long-term endpoints in the second cohort.
This finding matters because pericarditis risk stratification has historically leaned on imaging, etiology, and conventional CRP-based markers — tools that require specific testing infrastructure. NLR and SII are derived from routine complete blood counts, making them immediately accessible and essentially cost-free to calculate in any hospital setting worldwide. The dual-cohort design strengthens confidence, as independent replication is rare in inflammatory cardiac disease research. However, important caveats apply: both cohorts are retrospective and observational, limiting causal inference. The study cannot confirm whether the elevated NLR reflects pericarditis severity itself or underlying comorbid inflammatory burden — the adjusted models controlled for diabetes, renal disease, and malignancy, but residual confounding remains plausible. Cohort sizes are modest, and Asian-predominant populations may limit generalizability. As a preprint not yet peer-reviewed, these results should be considered preliminary. If prospectively validated, routine NLR calculation at admission could meaningfully sharpen triage decisions for pericarditis patients — an incremental but clinically actionable advance.