A D-dimer blood test checks for a small protein fragment called D-dimer. The test can help identify blood clotting problems. A positive result may suggest a blood clot has recently formed and broken down.

The blood’s clotting function is an important process that can help prevent a person from losing too much blood after an injury to a blood vessel. The body forms a blood clot when several proteins join together at the site of injury. Once the site heals, the body produces another protein to break the clot into small pieces. One of these protein fragments is known as a D-dimer.

D-dimer is not usually detectable in blood and is usually only present after the breakdown of a blood clot. Therefore, a doctor can use a D-dimer test to identify an increase in the body’s clotting mechanisms, which could help identify a coagulation disorder.

In this article, we will discuss what a D-dimer test is, what it can help detect, what to expect from the test, and how to interpret its results.

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A D-dimer test is a blood test that measures the level of D-dimer, a protein fragment that is present in blood after the breakdown of a blood clot. When blood clots break down, it produces fibrin degradation products (FDPs). One of these FDPs is known as D-dimer, which consists of variously sized pieces of crosslinked fibrin.

This test can be useful for indicating the presence of elevated clotting mechanisms and can assist a doctor in reaching a diagnosis. However, D-dimer tests are very sensitive and can result in false positives and negatives. As such, this means that further tests are necessary to accurately diagnose blood clotting disorders.

D-dimer tests could help doctors detect a variety of blood clotting disorders, which can include:

  • Pulmonary embolism (PE): Refers to a blockage in the pulmonary artery, which supplies the blood to the lungs. An embolism describes when a blood clot travels to the blood vessels of the lungs and becomes stuck. As this can cause problems with blood flow and gas exchange, it can become a life threatening event.
  • Deep vein thrombosis (DVT): Occurs when a blood clot, or thrombus, forms in a deep vein within the body. DVT can have serious consequences, as the blood clot can damage the valves in a vein. The clot may also break free and potentially result in a pulmonary embolism.
  • Disseminated intravascular coagulation: Describes a widespread hypercoagulable state, which may prevent blood from clotting normally. This can compromise blood flow and can result in multiple organ dysfunction.

A doctor may request a D-dimer test when they suspect a person may have a blood clotting problem. They may particularly recommend a test if an individual presents with DVT or PE symptoms, such as pain and swelling in the affected limb or labored breathing and chest pain.

Additionally, as it is a quick and noninvasive test, they may also use it to help rule these conditions out. A healthcare professional may also order this test along with other blood tests to help reach a diagnosis.

If a person is undergoing treatment for DIC, a doctor may use a D-dimer test to help monitor a person’s condition.

To perform a D-dimer test, a doctor will require a blood sample. They will typically draw the blood sample through a needle from a vein in the arm. As with any test that involves needles, it may carry a small risk of bleeding, infection, or bruising. An individual may feel a slight stinging or painful sensation at the site where they collect the sample. They do not need to prepare anything prior to the test.

After collecting the sample, the doctor or nurse will send it to a laboratory. Lab workers will then test the blood sample for the presence of D-dimers, before returning the results to the doctor. The doctor then organizes an appointment with the individual, where they may discuss the results and any further steps.

A 2021 paper notes that a typical D-dimer blood level is less than 0.50. As such, a doctor will consider a score of 0.50 or higher as a positive result.

A positive result indicates atypically high levels of proteins that relate to blood clot formation and breakdown, which could suggest a blood clotting condition. A typical result likely means a person does not have an acute blood clot or condition causing atypical clot formation and breakdown.

While D-dimer tests are very sensitive, meaning they often pick up existing blood clotting problems, they are not very specific, which means they may provide a positive result when no disease is present. A wide variety of factors can cause elevated D-dimer levels, including:

  • pregnancy
  • cigarette smoking
  • physical trauma
  • cancer
  • infections
  • sepsis
  • being older
  • being immobile
  • having an autoimmune disease

Many healthcare professionals may consider D-dimer as an additional test. When a doctor discerns that an individual has elevated D-dimer levels, they will request further testing to reach an accurate diagnosis.

Blood clotting is a vital process that can prevent excessive bleeding. When there is damage to a blood vessel, it gets smaller to let less blood through. Next, platelets immediately adhere to the injury and release chemicals that attract even more platelets, forming a platelet plug.

Finally, clotting factor proteins work together to form threads of a protein known as fibrin. The fibrin threads then weave over the platelet plug to create a strong clot, which allows the body to heal the injured blood vessels. As part of the healing process, the body then begins to break down the fibrin clot, which releases proteins such as D-dimer.

Factors that can increase the risk of developing a blood clot can include:

  • obesity
  • pregnancy
  • being immobile
  • smoking
  • oral contraceptives
  • certain cancers
  • trauma
  • certain surgeries
  • older age
  • family history of blood clots
  • chronic inflammatory diseases
  • diabetes
  • hypertension
  • high cholesterol

D-dimer is a blood test that can detect proteins present after the formation and breakdown of a blood clot. It can help doctors diagnose coagulation conditions that may affect blood clotting. While the test is quick, noninvasive, and sensitive, it is also not very specific. This means that while it can be a useful test in the diagnostic process, a doctor will request other tests to help them reach an accurate diagnosis.