Inflammatory biomarkers and hospitalization duration in children with iron deficiency anemia

Complete blood count (CBC)-derived inflammatory indices are increasingly used as inexpensive markers of systemic inflammation, but their incremental prognostic value in hospitalized children with iron deficiency anemia (IDA) remains uncertain. We evaluated whether these indices provide prognostic information beyond routinely available clinical factors, ferritin, and C-reactive protein (CRP) for hospitalization duration. This retrospective cohort study included 1004 children aged 2 months–15 years hospitalized with laboratory evidence of IDA at a tertiary pediatric hospital in Vietnam. The primary outcome was prolonged hospitalization, defined as length of stay (LOS) ≥ 7 days. Sequential multivariable logistic regression models incorporated demographic and clinical characteristics, ferritin, CRP, and individual CBC-derived inflammatory indices, including neutrophil-to-lymphocyte ratio, monocyte-to-lymphocyte ratio, platelet-to-lymphocyte ratio, systemic immune-inflammation index, and systemic inflammatory response index. Model performance was assessed using repeated cross-validation, receiver operating characteristic analysis, and sensitivity analyses using alternative LOS definitions and continuous LOS. The median LOS was 5 days (interquartile range, 4–6), and 20.9% of patients experienced prolonged hospitalization. Clinical characteristics, particularly admission department and underlying diagnostic category, accounted for substantial variation in hospitalization duration. CRP showed the strongest independent association with prolonged hospitalization, whereas the association with ferritin was attenuated after adjustment for CRP. None of the CBC-derived inflammatory indices provided significant incremental prognostic information. Cross-validated discrimination remained modest (mean AUC approximately 0.57–0.58). Sensitivity analyses generally supported the direction of the primary findings, although estimates were less precise at higher LOS thresholds. CBC-derived inflammatory indices provide little incremental prognostic information for hospitalization duration beyond clinical factors and CRP in hospitalized children with IDA. Although CRP was independently associated with prolonged hospitalization, overall predictive performance remained modest, underscoring the multifactorial nature of LOS and the limited value of admission inflammatory biomarkers alone for risk stratification.