How Do Doctors Diagnose a Pulmonary Embolism?

Medically Reviewed by James Beckerman, MD, FACC on December 06, 2022
2 min read

If you think you have a pulmonary embolism (PE), you should get medical help right away.

Your doctor will likely start with a physical exam. They’ll look closely at your legs to see if they’re swollen, tender, discolored, or warm. These are signs that you may have a clot deep in one of your veins.

Next, your doctor may order a number of tests, like a chest X-ray or ultrasound. You might also have blood tests. These can measure the amount of oxygen and carbon dioxide in your blood. They can also help your doctor detect a substance called D dimer. This is a small protein fragment that’s present in the blood after a clot is broken down by the body.

Other tests your doctor might order include:

  • Computed tomographic pulmonary angiography (CTPA). This is a special type of X-ray test. It’s also the main one doctors use to see if you have a PE. Your doctor will inject dye (“contrast”) into your veins. They’ll be able to see the blood vessels in your lungs on the X-ray.
  • Ventilation/perfusion (V/Q) scan. This test is used if the CTPA isn’t available, or isn’t a good match for you. It uses a radioactive material to show which parts of your lungs are getting air flow (ventilation) and blood flow (perfusion). If there’s low blood flow to a certain area, but the air flow is normal, a clot may be present.
  • Catheter-based pulmonary angiography. This is the most accurate test to detect PE. It may be used if other tests haven’t shown clear results. A specialist inserts a long, thin tube (catheter) into a large vein in your groin and into the arteries within your lung. They then inject dye through the catheter. Images of the blood vessels inside the lung will pop up on an X-ray. This is now only very rarely used because of CTPA.”
  • MRI. This may be a good option if you’re pregnant or your doctor is concerned that other tests that use contrast might be harmful to you.
  • Echocardiogram. This is an ultrasound of the heart. It can’t detect a PE, but it does show if you have strain on your heart caused by one.