It is a clinical prediction rule that assigns points based on signs, symptoms, and risk factors to estimate the likelihood of DVT. The score ranges from −2 to 9 and categorizes patients into low (≤0), moderate (1–2), or high (≥3) probability groups.

Low probability: check D-dimer — if negative, DVT is effectively ruled out. Moderate probability: D-dimer or ultrasound. High probability: proceed directly to compression ultrasound regardless of D-dimer. Clinical judgment should always supplement the score.

D-dimer is a blood test that measures a protein fragment produced when blood clots dissolve. A negative D-dimer in a low-risk patient effectively rules out DVT (high negative predictive value). However, D-dimer can be elevated in many conditions and has low specificity.

Common symptoms include unilateral leg swelling, pain or tenderness (especially in the calf), warmth, redness, and visible superficial veins. However, DVT can also be asymptomatic. Risk factors include recent surgery, immobilization, cancer, obesity, and hormonal therapy.