Predictors of Acute Pyelonephritis in Infants Less Than 4 Months Old with Febrile Urinary Tract Infection

Background: Detecting early predictors of acute pyelonephritis (APN) is essential for the prognosis, but few studies have focused on young infants specifically. Objectives: The aim of our research was to determine the relationship between APN and laboratory parameters in the age group less than 4 months. Methods: This retrospective study included patients aged less than 4 months with first time febrile urinary tract infection (UTI) between January 2012 and December 2018. White blood cells (WBC), C-reactive protein (CRP), and blood neutrophil/lymphocyte ratio (NLR) were analyzed. Patients were divided into two groups according to the presence of renal defects on dimercaptosuccinic acid (DMSA) scans. Results: In total, 205 patients were screened; 107 patients were in the APN group, and 98 patients were in the non-APN group. Compared with the non-APN group, the APN group showed significant differences in therapeutic response time (TRT), CRP, and NLR (all P values < 0.001). Multiple logistic regression analysis revealed that CRP, NLR, and TRT were independent risk factors for APN (P ≤ 0.001, 0.003, and 0.004, respectively). The area under the receiver operating characteristic (ROC) curve was 0.774 for CRP (P < 0.001). The optimum cut-off value for CRP was 4.27 mg/dL, with the highest sensitivity and specificity (70.1% and 73.5%, respectively). Conclusions: In the age group less than 4 months, without the image diagnosis, we could treat the patients as APN for longer antibiotic duration if CRP ≥ 4.27 mg/dL.