Investigations

Look for severe changes (irregular mucosal contour, > 2 mm deep ulceration, or ulceration undermining the mucosa). 

Why?

Ulcerative colitis: lack of severe changes on air enema reduces the risk of deep ulceration

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
suspected deep ulceration b (pre-test probability: 68%)	deep ulceration (histology)	air enema	3.6 (1.6 to 8.6)	88%	0.12 (0.040 to 0.37)	20%