Rule out emergent causes of abdominal pain such as appendicitis, small bowel obstruction, bowel perforation, etc.
Depending on presentation, chemistry panel and/or abdominal imaging may be appropriate in the emergency department setting
History and physical
Assessment of volume status
CBC to look for evidence of iron deficiency anemia
CMP
VBG
Lactic acid
Celiac disease
Acute diarrhea
Crohn's disease
Chronic diarrhea
Gastroesophageal reflux disease
Irritable bowel syndrome
Small intestinal bacterial overgrowth
Post-infectious irritable bowel syndrome