Your doctor will diagnose deep vein thrombosis (DVT) based on your medical history, a physical exam, and test results. He or she will identify your risk factors and rule out other causes of your symptoms. For some people, DVT might not be diagnosed until after they receive emergency treatment for pulmonary embolism (PE). Medical History To learn about your medical history, your doctor may ask about: Your overall health Any prescription medicines youre taking Any recent surgeries or injuries youve had Whether youve been treated for cancer Physical Exam Your doctor will check your legs for signs of DVT, such as swelling or redness. He or she also will check your blood pressure and your heart and lungs. Diagnostic Tests Your doctor may recommend tests to find out whether you have DVT. Common Tests The most common test for diagnosing deep vein blood clots is ultrasound. This test uses sound waves to create pictures of blood flowing through the arteries and veins in the affected leg. Your doctor also may recommend a D-dimer test or venography (ve-NOG-rah-fee). A D-dimer test measures a substance in the blood thats released when a blood clot dissolves. If the test shows high levels of the substance, you may have a deep vein blood clot. If your test results are normal and you have few risk factors, DVT isnt likely. Your doctor may suggest venography if an ultrasound doesnt provide a clear diagnosis. For venography, dye is injected into a vein in the affected leg. The dye makes the vein visible on an x-ray image. The x ray will show whether blood flow is slow in the vein, which may suggest a blood clot. Other Tests Other tests used to diagnose DVT include magnetic resonance imaging (MRI) and computed tomography (to-MOG-rah-fee), or CT, scanning. These tests create pictures of your organs and tissues. You may need blood tests to check whether you have an inherited blood clotting disorder that can cause DVT. This may be the case if you have repeated blood clots that are not related to another cause. Blood clots in an unusual location (such as the liver, kidney, or brain) also may suggest an inherited clotting disorder. If your doctor thinks that you have PE, he or she may recommend more tests, such as a lung ventilation perfusion scan (VQ scan). A lung VQ scan shows how well oxygen and blood are flowing to all areas of the lungs. For more information about diagnosing PE, go to the Health Topics Pulmonary Embolism article. 
How to diagnose Deep Vein Thrombosis ?