Neutrophil-to-Lymphocyte Ratio in Pediatric Anaphylaxis: A Potential Indicator of Cardiovascular Involvement

Background: The diagnostic utility of the neutrophil-to-lymphocyte ratio (NLR) in anaphylaxis is often obscured by the rapid immunomodulatory effects of epinephrine and corticosteroids. We evaluated NLR as a marker of reaction severity and clinical phenotype in pediatric anaphylaxis, employing a strict sampling protocol to minimize treatment-induced leukocytosis. Methods: This retrospective cohort study analyzed 81 children meeting EAACI anaphylaxis criteria. To isolate the intrinsic inflammatory signal, blood samples were included only if obtained within 30 minutes of epinephrine and 1 hour of systemic corticosteroid administration. Acute-phase NLR was compared to patient-specific healthy baselines, clinical severity grades, anaphylaxis triggers and acute serum tryptase levels. Results: Paired analysis (n=68, patients with both acute and healthy-state CBCs) confirmed a significant acute inflammatory response; acute NLR (median 1.10) was significantly elevated compared to healthy baselines (median 0.97; p=0.032). Although NLR failed to statistically discriminate between broad severity groups (mild-to-moderate vs. severe; p=0.40), phenotypic analysis revealed that patients with cardiovascular involvement exhibited numerically higher NLR values compared to those without. This pattern was mirrored by the trigger analysis, where NLR was significantly higher in drug-induced anaphylaxis than in food-induced reactions (median 2.64 vs. 0.92; p<0.001). Furthermore, patients with elevated acute serum tryptase (≥11.4 ng/mL) had significantly higher NLR values (p=0.038), reinforcing the association between intense neutrophilic mobilization and systemic instability. Conclusion: Although NLR does not align with standard clinical severity grading in a general pediatric cohort, it serves as a sensitive gauge of the systemic magnitude of anaphylaxis. Elevated NLR specifically reflects the intense hemodynamic stress associated with drug-induced phenotypes and massive mast cell degranulation. Thus, rather than a general severity stratification tool, NLR should be interpreted as a biological "red flag" for cardiovascular compromise, particularly in drug-induced cases, warranting early cardiac monitoring.