A biomarker is defined as “a characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention.”14 To differentiate between lower UTI and pyelonephritis, biomarkers like erythocyte sedimentation rate (ESR), C-reactive protein (CRP) and white blood count (WBC) have been studied in children. This evidence concerns the gene CRP and pyelonephritis.