How Pulmonary Embolism Is Diagnosed

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Pulmonary embolism is a common medical disorder that can have serious consequences. Appropriate treatment, delivered expeditiously, is important for optimizing the chances of a full recovery. Giving the appropriate treatment requires making the correct diagnosis as quickly as possible.

That being said, making a quick and accurate correct diagnosis of pulmonary embolus can be tricky. The most definitive tests for pulmonary embolus can be time-consuming, expensive, and entail at least some clinical risks. Doctors tend to weigh the risks and benefits before deciding what kind of testing is appropriate in a given circumstance.

Over time, experts have developed a three-step approach designed to rapidly rule out or diagnose a pulmonary embolus without exposure to unnecessary testing. If your doctor suspects you may have had a pulmonary embolus, you can expect him or her to use this three-step diagnostic approach:

pulmonary embolus diagnosis
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Step One

In step one the doctor quickly assesses the likelihood that a pulmonary embolus has occurred. They will make this assessment by taking into account the described symptoms and the clinical circumstances in which the occurred.

Several scoring systems have been devised for estimating the probability of a pulmonary embolus. The system used most often is the Wells scoring system, which takes into account whether:

  • Symptoms suggesting deep vein thrombosis are present
  • All other possible diagnoses seem less likely than a pulmonary embolus
  • Heart rate is over 100 beats per minute
  • A history of recent surgery or other immobilization
  • A prior history of diagnosed deep vein thrombosis or pulmonary embolus
  • Presence of hemoptysis (coughing up blood)
  • Presence of cancer

Point scores are assigned to each of these seven factors and an overall Wells score is computed.

With the Wells score in hand, a doctor can determine whether the probability of a pulmonary embolus is low, intermediate, or high.

Pulmonary Embolus Rule-Out Criteria (PERC)

If it turns out there is only a low probability of pulmonary embolus based on this clinical assessment, the doctor may also apply an additional scoring system: the PERC system.

The PERC system can determine whether the probability of a pulmonary embolus is so low that further testing should be stopped altogether. It consists of eight criteria:

  • Age under 50
  • Heart rate under 100
  • Blood oxygen saturation at least 95%
  • No hemoptysis
  • No estrogen use
  • No history of deep vein thrombosis or pulmonary embolus
  • No leg swelling
  • No surgery or trauma requiring hospitalization over past four weeks

If all eight criteria of the PERC score are present, no further testing for pulmonary embolus is recommended since the risk associated with additional testing will substantially outweigh the risk of missing a pulmonary embolus.

Step Two

If the probability of a pulmonary embolus in step one is determined to be intermediate, or if the clinical probability of pulmonary embolus is low but the PERC criteria have not been met, the next step is to obtain a D-dimer blood test.

The D-dimer test measures whether there has been an abnormal level of clotting activity in the bloodstream, such as would certainly be present if a person has had a deep vein thrombosis or pulmonary embolus.

If the clinical probability of PE is low or intermediate and the D-dimer test is negative, a pulmonary embolus generally can be ruled out and the doctor will move on to consider other potential causes for symptoms. 

A D-dimer test can be used only to rule out a pulmonary embolus, not to make the diagnosis. So if the D-dimer test is positive (or if a person’s clinical probability of a pulmonary embolus was deemed to be high in step one), it is time for step three.

Step Three

Step three involves a diagnostic imaging study. Generally, one of three kinds of tests will be used.

CT Scan

computerized tomography (CT) scan is a computerized X-ray technique that allows a doctor to examine the pulmonary arteries for an obstruction caused by a blood clot. A contrast agent is injected into the bloodstream during the test to help visualize the arteries.

A CT scan is accurate more 90% of the time in detecting a pulmonary embolus and is considered to be the test of choice if imaging is required to make the diagnosis.

V/Q Scan

A V/Q scan (also called the ventilation/perfusion scan) is a lung scan that uses a radioactive dye injected into a vein to assess the flow of blood to lung tissue. If a pulmonary artery is partially blocked by an embolus, the corresponding portion of lung tissue receives less than the normal amount of the radioactive dye.

The V/Q scan is typically only used for people who should not be exposed to all the radiation required by a CT scan as well as for people who have had an inconclusive CT scan.

Pulmonary Angiogram

For decades, the catheterization study known as the pulmonary angiogram was the gold standard for diagnosing a pulmonary embolus, but this test has now been supplanted by the CT scan.

For a pulmonary angiogram, dye is injected through a catheter placed into the pulmonary artery so that blood clots can be visualized on an X-ray.

This invasive test may still be required on occasion if a CT scan or a V/Q scan cannot be used or the results from these tests are inconclusive.

In Unstable People

A pulmonary embolus may cause immediate cardiovascular collapse. In fact, a pulmonary embolus often turns out to be the cause of sudden death in younger people.

If an individual has severe cardiovascular instability and a pulmonary embolus seems likely to be the cause, an organized three-step diagnostic plan is not feasible. For them, treatment likely will be administered immediately, along with other resuscitative efforts, before a definitive diagnosis of pulmonary embolus can be made.

Differential Diagnosis

In diagnosing a pulmonary embolus, it is important to rule out other medical diagnoses whose symptoms can be similar to those of a pulmonary embolus. Conditions that need to be considered (that is, the differential diagnosis) often include heart attacksheart failurepericarditiscardiac tamponade, pneumonia, and pneumothorax.

The electrocardiograms, chest X-rays, and echocardiograms that are often obtained during routine clinical evaluations for suspected heart or lung disorders are usually enough to rule out these other conditions.

Even if one of these other diagnoses is made, it does not necessarily mean that a pulmonary embolus is ruled out, because a person may have two conditions at the same time—and many cardiovascular diseases increase the risk of pulmonary embolus. So if there is still reason to suspect a possible pulmonary embolus after another diagnosis is made, it is important to take the additional steps necessary to complete diagnostic testing.

In the some cases, a pulmonary infarction is diagnosed as an additional finding when looking for a pulmonary embolus.

Frequently Asked Questions

Do I need an X-ray to diagnose a pulmonary embolism?

Usually, a special type of X-ray is done to confirm whether you have a pulmonary embolism. Known as a computed tomographic pulmonary angiography (CTPA), this scan requires dye to be injected into a vein in order to capture an image of the blood vessels in the lungs. 

What kind of blood test is used to detect a pulmonary embolism?

A D-dimer test can check for substances that indicate a blood clot has broken down. If you’re diagnosed with a pulmonary embolism, other blood tests will be ordered to determine if you’ve suffered heart damage from the embolism.

Can other conditions be mistaken for a pulmonary embolism?

Other conditions can have similar symptoms. These include heart attack, heart failure, pericarditis, pneumonia, and hyperventilation. Because your doctor needs to rule out these other problems and because pulmonary embolism can be hard to diagnose, you may need to undergo several tests before the diagnosis is confirmed.

 

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