Investigations

• abdominal ultrasound scan ^b looking for 
  • target appearance of bowel (strong echogenic centre with a sonolucent rim > 0.5 cm diameter) ± stenosis 
  • distended fluid-filled loops, luminal narrowing, movement of echogenic particles or stiff loops

Why?

A normal abdominal ultrasound scan makes Crohn's disease less likely

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
suspected inflammatory bowel disease b (pre-test probability: 50%)	Crohn's disease (histology, endoscopy, radiology and clinical findings)	abdominal ultrasound scan	4.9 (3.1 to 7.6)	83%	0.19 (0.12 to 0.31)	16%