Clinical exam
Risk stratification for further testing indicated using, e.g. Modified Wells Score
Can be applied for patients whose clinical presentation is concerning for a<unk>  in order to risk stratify.
Active cancer (<6 mo) (1pt)
Paralysis, paresis, or immobility of extremity (1pt)
Bedridden >3 days because of symptoms within 4 weeks (1pt)
TTP along<unk><unk>  system (1pt)
Entire leg swollen (1pt)
Unilateral calf swelling >3cm below tibial tuberosity (1pt)
Unilateral pitting edema (1pt)
Collateral superficial veins, not varicose (1pt)
Previously documented<unk>  (1pt)
Alternative diagnosis as likely or more likely than<unk>  (-2pts)
Scoring:
A score of 0 or lower → minimal risk -<unk>  prevalence of 5%. D-dimer testing is safe in this group - negative d-dimer decreases the probability of disease to <1% allowing an ultrasound to be deferred.
A score of 1-2 → moderate risk -<unk>  prevalence of 17%. D-dimer testing still effective and a negative test decreases post-test probability disease to <1%
A score of 3 or higher → high risk -<unk>  prevalence of 17-53% → patients should receive an ultrasound
Requires ultrasound for diagnosis.  Cannot be ruled out with d-dimer.

Generally involves axillary or subclavian veins
Primary upper extremity<unk>  typically presents in young healthy individuals
Secondary upper extremity<unk>  often due to indwelling catheters
Obtain a chest x-ray to rule out bony abnormalities that may be causing<unk>  obstruction
Deep venous thrombosis
Arterial thrombosis
Venous thromboembolism
Arteritis
Lymphangitis
Arthritis
Phlebitis
Buerger disease