WELL's score is an algorithm used to decide what group to place the patient in according to risk of developing the disease (high risk, intermediate or low). Well's score includes points for: active cancer, history of paralysis, immobilization, tenderness along limb, swelling of entire limb, swelling of limbs compared to the other, pitting edema, dilated superficial vessels, previous history of DVT, presence of alternate diagnosis. If the score is zero= low probability, 1-2 intermediate probability and 3 or more = high probability. If patient has high probability, should get an ultrasound done. If low or intermediate, do D-dimers. If D-dimers are high, then get an USG done. D-dimers are the byproducts of fibrin breakdown and are used to diagnose DVT.