Your doctor will ask about your symptoms and medical history, and perform a physical exam. So called "stress tests" are commonly employed in the diagnosis of TOS.
During these tests, your doctor will ask you to hold your arms and head in positions that may cause the TOS symptoms to reappear. The results of these tests will help determine whether you have TOS and rule out other possible related conditions.
Rarely, arteriography is used to evaluate TOS. This is an invasive procedure where dye is injected into the arteries to evaluate for any abnormalities. This may be used if a surgery is being planned to correct an arterial TOS.