How Blood Clots Are Diagnosed

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The blood clotting mechanism is vitally important to life. When a blood vessel is damaged by injury, the normal clotting mechanism ensures that blood loss will be limited. Furthermore, the blood clot that forms at the site of injury provides the body’s first step toward healing.

However, if a blood clot forms when it should not, serious problems can result, because the clot can lead to significant damage to the organ supplied (or drained) by the blocked vessel.

This is why diagnosing a blood clot—which is possible with lab and imaging tests—is so important.

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When to Diagnose a Blood Clot

Two types of blood clots that can lead to serious damage include thrombi and emboli. A thrombus is a blood clot that forms within a blood vessel, and an embolus is a blood clot that travels through a blood vessel and causes blockage at its destination.

Blood clots cause damage to the tissue because they can block blood flow through a vessel. When the tissue is deprived of the oxygen and nutrients that it should get from blood, serious damage can occur, such as with a stroke. Diagnosis often begins with symptoms of organ damage.

Common medical conditions that are very often due to either thrombus or embolus include the following.

  • Stroke is most often caused either by thrombosis of one of the arteries that supply the brain, or an embolus that travels to the brain (most often from the heart or carotid artery).
  • Heart attack is usually due to an atherosclerotic plaque, which causes a thrombus to form within a coronary (heart) artery.
  • Deep vein thrombosis (DVT) is a clot that forms in one of the major veins of the leg, thigh, or pelvis.
  • Pulmonary embolus is a blood clot that travels to the lungs, usually from a DVT.
  • Other conditions include thrombosis of the major vein that drains the liver (portal vein thrombosis), thrombosis of the vein that drains a kidney (renal vein thrombosis), and embolization of a clot to an arm or leg.  

Before effective treatment can be administered, it is important to determine whether a blood clot is actually causing the problem. Treatments for blood clots often include powerful blood thinners. While these medications can be effective for dissolving a clot or preventing it from growing—they can cause side effects, such as bleeding.

Blood Clots Healthcare Provider Discussion Guide

Get our printable guide for your next healthcare provider's appointment to help you ask the right questions.

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Lab Tests

Lab tests for diagnosing a blood clot can measure abnormal activation of the blood clotting system and offer clues that will help your healthcare provider narrow down your diagnosis.

D-Dimer Blood Test

The D-dimer blood test detects whether there has recently been an abnormal level of clotting activity somewhere within the bloodstream. This test is the most useful in helping healthcare providers pin down their suspicion that either DVT or pulmonary embolus has occurred.

Cardiac Biomarkers

Cardiac biomarkers are used to help diagnose a heart attack. These blood tests do not strictly diagnose blood clots; rather, they detect whether heart muscle damage has occurred—which is almost always caused by dislodging of a coronary artery plaque, along with subsequent thrombosis formation.

Imaging Tests

Your healthcare provider will order the imaging tests they deem necessary for making a proper diagnosis. Some of these tests can identify a blood clot, some can detect damage due to a blood clot, and some can determine whether you are at risk of having a blood clot.

Ask your healthcare provider what the test is intended to reveal, and ask any questions you have about the procedure.

Compression Ultrasound

The compression ultrasound test is a noninvasive test that can be performed at the bedside that is often very useful in diagnosing a DVT. 

V/Q Scan

A ventilation perfusion scan (V/Q scan) is a test using a radioactive dye to examine blood flow to the lungs in order to detect whether a pulmonary blood vessel has been blocked by a pulmonary embolus.

CT Scan

The computerized tomography (CT) scan is a computerized X-ray technique that can show anatomic detail. The CT scan may detect the brain damage of a stroke or the lung damage of a PE.

MRI Scan

MRI scans can be used to detect early organ damage due to a stroke, PE, portal vein thrombosis, or renal vein thrombosis. These tests take longer than CT scans, so when time is of the essence, CT scans may be used instead.

Angiography or Venography

These are catheterization techniques in which a dye is injected into a blood vessel where a clot is suspected and images of the blood vessel are taken.

Pulmonary angiography can be used to diagnose a pulmonary embolus, whereas venography is used to diagnose DVT. Cardiac angiography examines the coronary arteries, and carotid angiography can detect damage or a clot in the carotid artery—a blood vessel in the neck.

Echocardiography

Echocardiograms are often used to assess the risk of an embolic stroke.

The echocardiogram can detect a thrombus that has formed in the heart (typically in the left atrium in a person with atrial fibrillation, or in the left ventricle in a person with severe dilated cardiomyopathy). The echocardiogram can also detect cardiac problems that can allow an embolus to traverse the heart, such as a patent foramen ovale.

Frequently Asked Questions

  • Can a blood test show a blood clot?

    Yes, the D-dimer blood test can be used to help determine if a blood clot has occurred, such as a deep vein thrombosis (DVT) or pulmonary embolus (PE). Cardiac biomarkers can also help healthcare providers see if damage to the heart muscle has occurred, which may hint that a blood clot has developed in the blood vessels of the heart.

  • Which tests can look for a blood clot in the leg?

    Lab tests and imaging tests can provide clues to a blood clot in the leg or DVT elsewhere in the body.

    Your healthcare provider may order any of the following tests:

  • Which tests can look for a blood clot in the lungs?

    To look for evidence of a blood clot that has affected the lungs (PE), healthcare providers will usually order one or more of the following imaging tests:

    • V/Q scan
    • Pulmonary angiography
    • Computed tomography (CT) scan
    • Magnetic resonance imaging (MRI) scan
  • How can I tell if I have a blood clot?

    While it's possible to have a blood clot without symptoms, certain warning signs may occur:

    • Skin tenderness, redness, and warmth in an area of the body
    • Swelling (typically affecting one leg, but not the other)
    • Shortness of breath
    • Chest pain
    • Dizziness
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11 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  7. Centers for Disease Control and Prevention. Diagnosis and treatment of venous thromboembolism. Updated March 14, 2019.

  8. Stein PD, Yaekoub AY, Matta F, et al. Resolution Of Pulmonary Embolism On Ct Pulmonary Angiography. Ajr Am J Roentgenol 2010; 194:1263. doi:10.2214/AJR.09.3410


  9. National Heart, Lung, and Blood Institute. Venous Thromboembolism.


  10. National Blood Clot Alliance. Signs and symptoms of blood clots.

  11. Texas Heart Institute. Heart attack warning signs.

Additional Reading