Arteries are the thick walled and more circular vessels identified
Doppler flow can be used to identify different directions of flow in vessels and to identify no vascular structures
Noncompressible vein may be mistaken for an artery, leading to a false negative result
An artery may be mistaken for a non-compressible vein, leading to a false positive result
Lymph nodes may be confused with noncompressible vein and if found, can be identified by moving up or down 1 cm
Does not rule out calf<unk> s
For a more thorough exam, scan from the saphenofemoral junction down through the adductor canal in addition to the areas described above
Use a curvilinear probe for obese or edematous patients
An appropriate amount of pressure gives complete collapse of the vein as well as some (but not full) compression of the adjacent artery.
DVT ultrasound
Ankle-brachial index
Thromboelastography 
IVC ultrasound
D-dimer
Aortic ultrasound
Bubble study
Age adjusted D-dimer