Fig. 1

The four steps of a test-treatment strategy using abdominal CT to diagnose appendicitis in patients presenting with right lower quadrant abdominal pain. The trial compared two diagnostic strategies for confirming or ruling out suspected acute appendicitis in adults presenting to the emergency department with right lower quadrant abdominal pain [18]. The routine approach of scanning all such patients with CT was compared with a new strategy of ordering CT only when indicated by specific signs and symptoms. In both arms the 4 test-treatment steps consist of testing (routine laboratory tests +/− a CT scan), a diagnostic decision (appendicitis, other disease, no disease), a management plan for each group (surgery or antibiotics to treat appendicitis, discharge for disease free patients, and treatment as necessary for alternative conditions), and delivery of these treatments. The trial’s primary outcome measured the proportion of removed appendices that were disease-free