A blood clot in a deep vein of the leg, called deep vein thrombosis (DVT), can be dangerous because part of the clot can break off and travel to the lungs, causing a pulmonary embolism.
Here are 10 warning signs of a possible DVT:
- Swelling in one leg, especially in the calf or thigh.
- Pain or tenderness in the leg, often described as a cramp or soreness.
- Warm skin over the affected area.
- Red or discolored skin on the leg.
- A swollen vein that is more visible than usual.
- Pain that worsens when standing or walking.
- A feeling of tightness or fullness in the affected leg.
- One calf appearing larger than the other.
- Tenderness when touching the calf, though this symptom alone is not specific.
- Symptoms occurring after prolonged immobility, such as a long flight, hospitalization, or surgery.
Risk factors
You may be at higher risk if you:
- Have recently had surgery or a major injury.
- Spend long periods sitting or lying down.
- Are pregnant or recently gave birth.
- Have cancer or are receiving cancer treatment.
- Smoke.
- Take estrogen-containing medications.
- Have obesity or a family history of blood clots.
When to seek medical care
A possible DVT should be evaluated promptly—ideally the same day—because treatment can reduce the risk of serious complications.
Call emergency services immediately if you have leg symptoms plus any of the following:
- Sudden shortness of breath.
- Chest pain, especially if it worsens with breathing.
- Coughing up blood.
- Fainting or feeling like you might pass out.
These may be signs of a pulmonary embolism, which is a medical emergency.
It’s important to remember that not everyone with a DVT has symptoms, and symptoms such as leg pain or swelling can also be caused by muscle injuries, varicose veins, or infections. A healthcare professional typically confirms the diagnosis with an ultrasound and, in some cases, blood tests.
