Investigations

Using the clinical prediction rule ranking, ^a read the IPG result as follows: 

High risk for DVT 

• Positive scan: DVT
• Negative scan: Venous thromboembolism remains so likely that a venogram is needed.
  • If the venogram is positive: DVT
  • If the venogram is negative: no DVT

• Positive scan: DVT
• Negative scan: Repeat the scan in one week and withhold anticoagulation.
  • If it is positive: DVT
  • If it is negative: no DVT

• Positive scan: Venous thromboembolism remains so unlikely that a venogram is needed.
  • If the venogram is positive: DVT
  • If the venogram is negative: no DVT
• Negative scan: no DVT

Why?

• Few DVT are missed - 1.1% ^a
• DVT is very rare if two scans are negative. ^a

Impedance plethysmography scan can help diagnose and exclude a DVT

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
suspected first DVT a (pre-test probability: 30%)	deep vein thrombosis (venogram)	impedance plethysmography	11 (8.8 to 150)	83%	0.20 (0.16 to 0.25)	8%