Rule out alternate etiologies for symptoms
Evaluate for complications (e.g. fistulae, abscess, obstruction)
Labs
CBC
Chemistry
ESR/CRP
Fecal calprotectin (sensitive indicator of intestinal inflammation, unreliable in select<unk> 's patients)
C.diff toxin
Type and screen if any bleeding suspicion
Consider imaging:
Plain abdominal films - rule out small bowel obstruction, perforation and toxic megacolon
CT A/P
Most useful diagnostic test in patients with acute symptoms who have known or suspected<unk> 
Findings: bowel wall thickening, mesenteric edema, local abscess, fistulas
CBC
Chemistry
ESR/CRP
Fecal calprotectin (sensitive indicator of intestinal inflammation, unreliable in select<unk> 's patients)
C.diff toxin
Type and screen if any bleeding suspicion
Plain abdominal films - rule out small bowel obstruction, perforation and toxic megacolon
CT A/P
Most useful diagnostic test in patients with acute symptoms who have known or suspected<unk> 
Findings: bowel wall thickening, mesenteric edema, local abscess, fistulas
Most useful diagnostic test in patients with acute symptoms who have known or suspected<unk> 
Findings: bowel wall thickening, mesenteric edema, local abscess, fistulas
Crohn's disease
Viral gastroenteritis
Irritable bowel syndrome
Bacterial gastroenteritis
Ulcerative colitis
Campylobacter infections
Celiac disease
Clostridium difficile colitis