Investigations

• venography: ^a the reference standard 

Why?

• It is the current reference standard, but it is not perfect
  • Some DVT are missed: 2% of patients with a negative venogram develop DVT. ^c
  • It may not be technically possible (5%) ^c
  • Pain is a common side-effect (20%). Serious side-effects are rare. ^c
  • It may cause DVT. ^c