Investigations

There is little benefit in scanning asymptomatic high-risk patients (e.g. following orthopaedic surgery). ^a  

Why?

An ultrasound scan cannot safely diagnose and exclude an asymptomatic DVT

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
suspected asymptomatic first DVT a (pre-test probability: 27%)	deep vein thrombosis (venogram)	ultrasound scan	9.8 (7.6 to 13)	78%	0.60 (0.56 to 0.65)	18%