predictors and outcomes of nondiagnostic ultrasound for acute appendicitis in children ultrasound assessments of children with possible acute appendicitis aa are often nondiagnostic we aimed to identify the predictors of nondiagnostic ultrasound and to investigate the outcomes a retrospective review was conducted on children aged 4 to 17 years evaluated in 2013 for aa with ultrasound at a tertiary hospital pediatric emergency department demographics clinical data and outcomes were analyzed of 528 children 194 367 had diagnostic ultrasounds and 334 633 had nondiagnostic ultrasounds nondiagnostic ultrasounds were more common afterhours 7 pm7 am weekdays and on weekends 707 than during business hours 7 am7 pm weekdays 293 afterhours timing and female sex were identified as independent predictors of nondiagnostic ultrasounds p 005 for both aa was diagnosed in 35 children with a nondiagnostic ultrasound 105 p 005 no child who underwent a nondiagnostic ultrasound was found to have aa with laboratory values of white blood cell 11 103l and creactive protein crp 5 mgdl children with nondiagnostic ultrasounds have a low likelihood of aa if white blood cell 11 and crp 5 we propose a management algorithm that we hope will help reduce admissions and decrease the use of computed tomography scans