Investigations

• ANCA and ASCA (anti-Saccharomyces cerevisiae antibodies) in new cases ^{a c}

Why?

A positive ANCA or ASCA diagnoses inflammatory bowel disease

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
inflammatory bowel disease c   (pre-test probability: 50%)	inflammatory bowel disease (radiology, endoscopy and histology, negative culture)	p-ANCA	infinity (4.3 to infinity)	100%	0.61 (0.57 to 0.66)	39%
children with suspected inflammatory bowel disease a   (pre-test probability: 42%)	inflammatory bowel disease (colonoscopy and histology))	ASCA IgA > 20 or IgG > 40 EU/ml, or ANCA > mean 20 EU/ml	13 (4.8 to 33)	90%	0.33 (0.22 to 0.50)	20%