What's most likely signs of blood clots in the legs?

Swelling and pain: The most common symptoms of blood clots in the leg, otherwise known as venous thrombosis, are swelling and pain. Unfortunately, these are not very specific, & usually have other causes. A simple blood test called d-dimer can detect if you do not have a blood clot, but this test also has a lot ot false positive results. If the d-dimer is positive, the best way to rule out a clot is with ultrasound.