Blood clots typically form in the deep veins of the lower legs, and are called "deep vein thromboses" or "DVT." They may stay in the leg, or move to another part of the body such as the lungs, resulting in a what's called a pulmonary embolism. If the clot does not migrate from the site where it formed, such as the leg or arm, it will produce certain symptoms and signs. These are defined as what the patient describes and what the health care provider observes, respectively.
A blood clot in a vein of the lower leg, for example, will cause pain and swelling at the point distal to the clot, meaning farther from the heart. The arteries run down the leg to supply blood to the limb, and the veins run up the leg to return it to the heart. A clot at the knee will cause swelling and pain below the knee. According to FamilyDoctor.org, there may also be warmth and a change of color, usually redness.
Physical Exam Signs
Some of the physical exam signs will be the same as concerns raised by the patient, such as noticing that a leg is swollen, red, warm and tender. More objective analysis can be undertaken by measuring and comparing the circumference of each of the legs, or feeling the tracts of the veins to elicit tenderness. Homan's sign is pain with flexing the foot towards the knee, but is not very predictive of a DVT.
Laboratory findings are not specific to blood clots, but may raise the level of suspicion. A health care practitioner may check a complete blood count, which includes white blood cells, red blood cells and platelets. She may also check coagulation studies such as the PTT and the PT / INR, and D-dimers.
According to PreventDVT.org, radiologic signs are the most valid method for diagnosing most blood clots, especially a DVT. An ultrasound is a very common method, and is easy and painless. Another option that may be more sensitive for picking up blood clots below the knee is venography, in which dye is injected into the vein and then an X-ray is taken. A third possibility is an MRI.