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What are d-dimer tests and how reliable are they?

This article was published on
August 30, 2021

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D-dimer tests are used to rule out the possibility of blood clots among patients who typically have a low likelihood of blood clots. The test is used for screening purposes only, and additional tests would be required to confirm a diagnosis.

D-dimer tests are used to rule out the possibility of blood clots among patients who typically have a low likelihood of blood clots. The test is used for screening purposes only, and additional tests would be required to confirm a diagnosis.

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What our experts say

D-dimer tests look for serious blood clots that might occur due to medical conditions such as deep vein thrombosis (DVT) or pulmonary embolism (PE). A D-dimer test is a useful and reliable tool to rule out the presence of blood clots for people who are typically at low risk of blood clots. Given the link between COVID-19 and blood clots, D-dimer tests have often been used in emergency rooms.

A negative d-dimer test result means you likely do not have a serious blood clotting disorder, like a pulmonary embolism/deep vein thrombosis (PE/DVT). However, a positive or “high” test result does not necessarily mean you actually have a blood clot. Other tests are required to confirm the presence of a clot. Some clinical conditions may contribute to high D-dimer levels, including but not limited to recent surgery or heart disease. That is why a doctor would likely order additional tests to confirm a diagnosis in the event of a high or abnormal d-dimer test result.

In general, the reliability of a test depends on its sensitivity and specificity. Sensitivity measures the ability of a test to correctly identify an individual who has the disease. The D-dimer test happens to be highly sensitive, which means that there are few false negatives and few cases of disease are missed. Specificity refers to a test’s ability to accurately identify an individual who does not have the disease. The D-dimer test has poor specificity, and hence, is typically used as an initial screening test rather than to provide a confirmed diagnosis. The D-dimer test, in particular, is most reliable in individuals who have a low likelihood of pulmonary embolism/deep vein thrombosis. Given the characteristics of the test, it is safest to use as a screening test to rule out PE/DVT who would not normally be expected to have the condition.

Context and background

In patients with severe COVID-19 illness, PE/DVT can be one of the complications that increase a patient’s likelihood of dying from the illness. Ever since COVID-19 was initially detected in Wuhan, China, studies have shown a link between COVID-19 and a higher probability of blood clots.

Blood clots are a normal part of the body’s immune response to heal an open wound and prevent blood loss. In most patients, your body dissolves the blood clot after your injury is healed and produces proteins like D-dimer in the process. However, in patients with a prior history of blood clotting disorders or a serious COVID-19 infection, clotting can occur without a serious injury and leave elevated levels of D-dimer. The amount of D-dimer protein is highest in patients who are critically ill. In order to rule out the possibility of a blood clotting disorder, a doctor can take a blood sample and test for higher-than-normal levels of D-dimer, which is the primary function of D-dimer tests.

Resources

  1. Thromboembolism risk of COVID-19 is high and associated with a higher risk of mortality: A systematic review and meta-analysis (The Lancet
  2. Pharmacologic Thromboprophylaxis and Thrombosis in Hospitalized Patients with COVID-19: A Pooled Analysis (Thromb Haemost)
  3. D-dimer test (Medline Plus)
  4. Pulmonary Embolism and Increased Levels of D-Dimer in Patients with Coronavirus Disease (U.S. Centers for Disease Control)
  5. Effectiveness of D-Dimer as a Screening Test for Venous Thromboembolism: An Update (North American Journal of Medical Sciences)

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