Investigations

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

Why?

Impedance plethysmography 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: 7%)	deep vein thrombosis (venogram)	impedance plethysmography	3.8 (2.6 to 5.6)	53%	0.88 (0.84 to 0.92)	21%