1. History and physical exam. If your history and examination are suspicious that it might be a dvt, then you need a 2.
D-dimer. A blood test is done. If it is very low, you don't have a dvt. If it is high you might have a DVT and you need an 3. Ultrasound scan. This is the gold standard test. The ultimate way to check for a DVT is ultrasound.