Factors Associated with Long COVID in the Pediatric Population: A Retrospective Case–Control Study

Background: Long COVID in children is increasingly recognized, yet its clinical predictors and objective biological correlates remain insufficiently characterized. Objectives: The objective was to compare clinical, demographic, and laboratory characteristics between children with and without long COVID and to identify associated variables. Methods: We conducted a retrospective observational case–control study at the “Dr. Victor Gomoiu” Children’s Clinical Hospital, including pediatric patients with confirmed SARS-CoV-2 infection. Cases were defined as children with symptoms persisting ≥12 weeks after acute infection, while controls had no persistent symptoms at ≥12 weeks. Results: Eighty-nine children with long COVID and 88 matched controls were included. Children with long COVID were significantly older (1.79 ± 0.90 vs. 1.14 ± 0.80 years, p < 0.001) and more frequently from urban areas (86.5% vs. 69.3%, p = 0.0099). Lymphocyte, monocyte, and basophil counts were significantly lower in the Long COVID group, while D-dimer, ferritin, serum iron, urea, and creatinine levels were significantly higher. A multivariate predictive model demonstrated excellent discrimination (AUC = 0.94), with optimal sensitivity (84.3%) and specificity (89.8%) at a probability threshold of 0.48. Conclusions: Long COVID in children was associated with identifiable clinicobiological features. An exploratory composite model showed good discrimination but requires external validation.