How do you tell the difference between a calf strain and dvt?

Venous doppler study: The "gold standard" test would be a venous doppler study . Plus, a DVT would probably show some calf swelling/enlargement compared to the opposite side, which you probably would not see with a calf strain.

Ultrasound: If you really suspect that you have DVT or even superficial thrombophlebitis, an ultrasound or non-invasive scan would be the way to go to check for blood clots.

How to diagnose DVT.: The gold standard to diagnose DVT between the lower calf and groin is a venous duplex ultrasound. If this is negative then the chance of having DVT is usually less than 2%. A negative d-dimer would further substantiate no DVT. Sometimes it can be difficult to differentiate between DVT and a calf strain on physical exam alone.