Investigations

Why?

A positive helical CT scan makes a pulmonary embolism more likely

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
suspected pulmonary embolism and d-dimer > 50 microg/l a (pre-test probability: 40%)	pulmonary embolism (a validated algorithm including lower-limb compression ultrasonography, lung scanning and pulmonary angiography or follow-up for 3 months)	helical CT	8.0 (4.8 to 13)	84%	0.33 (0.25 to 0.44)	18%