urgent radiologic workup For example, abdominal pain and bilious vomiting in an infant requires supine and upright plain films, as well as a limited upper GI series for evaluation of congenital obstructive anomalies such as malrotation A child with paroxysms of colicky abdominal pain and grossly bloody stools requires immediate ultrasound for rapid diagnosis of intussusception, or in clearcut cases should proceed directly to an air-contrast enema for both diagnosis and reduction of the intussusception Other situations require no imaging studies (e.g., a typical case of viral gastroenteritis) In many cases, cultures or serum chemical analyses are essential for making a diagnosis (e.g., meningitis, aspirin toxicity, urinary tract infection [UTI], pregnancy) or for guiding management (e.g., degree of metabolic derangement in severe dehydration, pyloric stenosis, diabetic ketoacidosis) For most straightforward, common illnesses (e.g., gastroenteritis, respiratory infections with posttussive emesis), laboratory investigation is unwarranted