Background: Acute kidney injury (AKI) is a serious complication in adults with COVID-19. While lymphopenia indicates disease severity, its association with renal outcomes in pediatric COVID-19 remains unclear. This study compared AKI incidence, severity, and prognosis between lymphopenic and non-lymphopenic children hospitalized with COVID-19.

Methods: In this retrospective cohort study, medical records of children under five years (n=148) hospitalized with PCR-confirmed COVID-19 were reviewed. Patients were divided into lymphopenic (n=35) and non-lymphopenic (n=113) groups based on admission absolute lymphocyte count. AKI severity was classified using CTCAE v5.0. Data were analyzed using SPSS 25 with Chi-square, Mann-Whitney U, Fisher's exact tests, and multiple logistic regression.

Results: Overall AKI incidence was 9.5% (14/148). The lymphopenic group was significantly younger (P=0.031). AKI incidence was higher in the lymphopenic group (14.3%) than in the non-lymphopenic group (8.0%), but not significantly (P=0.321). No significant differences were found in AKI severity (P=0.627) or prognosis (P=1.000). Multiple regression showed lymphopenia, age, sex, and comorbidities were not independent predictors of AKI. Notably, mortality in children who developed AKI was alarmingly high (35.7%) compared to those without AKI (5.2%).

Conclusion: Although lymphopenia was not a significant predictor of AKI in this pediatric cohort, the strikingly high mortality associated with AKI underscores the critical need for rigorous renal function monitoring in all hospitalized children with COVID-19.