As there are many causes of a painful leg, a doctor cannot diagnose deep vein thrombosis (DVT) by symptoms alone. The doctor will ask you some questions and do a blood test (called D-dimer), and will then decide if further tests are required.
Before performing any tests, a doctor will establish the likelihood of a blood clot by asking questions, performing a physical examination, and completing a formalised risk score. If the probability of a DVT is low, a blood test, called a D-dimer test, is performed to rule out the diagnosis. If these tests show the probability of a DVT is high, additional tests, like an ultrasound will be performed to confirm the diagnosis.
Figure: compression ultrasonography involves pressing the ultrasound probe to the vein to check if it is open or obstructed by a thrombus.
Further imaging tests include taking X-rays of the veins with the use of contrast agents, as well as more sophisticated imaging such as computed tomography (CT) and magnetic resonance imaging (MRI).