BackgroundD-dimer, as well as other biomarkers related to coagulation, is significantly increased during severe bacterial infection and sepsis. The aim of this study was to evaluate the usefulness of serum D-dimer as a biological marker in diagnosing acute pyelonephritis (APN) and in predicting vesicoureteric reflux (VUR) in infants with urinary tract infection (UTI).MethodsWe retrospectively analyzed the data of 177 young infants (<2 years) with febrile UTI between 2005 and 2014, grouped as APN and lower UTI groups. Conventional inflammatory markers (white blood cell count (WBC), erythrocyte sedimentation rates (ESR), C-reactive protein (CRP)), and D-dimer were measured.ResultsThe WBC counts (P = 0.002), ESR (P < 0.0001), CRP (P < 0.0001), D-dimer levels (P = 0.006) and the presence of VUR (P < 0.0001) were significantly higher in the APN group than in the lower UTI group. Multiple logistic regression analyses showed that D-dimer (odds ratio [OR]:1.003, 95% CI: 1.001–1.006, P = 0.002) was an independent predictive factor for VUR in young children with UTI. The area under the curve (AUC) value from the receiver operating characteristic (ROC) curve of D-dimer (0.621, P = 0.046, 95% CI: 0.499–0.743) for prediction of VUR was higher than other inflammatory markers, but was inferior to CRP in predicting APN.ConclusionsOur results demonstrate that D-dimer can be used as an inflammatory marker in infants with febrile UTI in addition to other inflammatory markers.