D-dimer · What Is It, Testing, and More

High D-dimer levels (i.e., more than 0.5 μ/mL) may indicate conditions associated with abnormal blood clot formation, such as deep vein thrombosis (DVT), pulmonary embolism (PE), disseminated intravascular coagulation (DIC), or ischemic stroke. 

DVT occurs when a blood clot develops in a large vein of the upper or, most commonly, lower limbs, and its breakdown leads to elevated D-dimer levels. One of the most dangerous complications of DVT is PE, which occurs when a part of the blood clot breaks off and travels to the lungs. This is potentially life-threatening, as the clot obstructs pulmonary blood flow, preventing oxygenation and leading to sudden chest pain and shortness of breath.  

DIC is another possible cause of elevated D-dimer. DIC is a rare but life-threatening condition typically caused by an underlying disorder such as sepsis, cancer, trauma, postoperative damage, obstetric complications, or severe immune reactions (e.g., incompatible blood transfusion, organ transplant rejection, toxins from snake or spider venom). These conditions cause uncontrolled activation of the coagulation cascade, leading to the widespread formation of multiple intravascular clots. Paradoxically, this excessive clotting consumes platelets and clotting factors, ultimately resulting in uncontrolled, severe bleeding.  

High D-dimer levels can also be detected after an acute ischemic stroke (i.e., neurological deficits resulting from obstructed blood supply to part of the brain) and have been shown to be correlated with long- and short-term prognosis.  

However, an elevated D-dimer is not specific to thromboembolic events and can also result from other conditions, including advanced age, smoking, obesity, pregnancy or childbirth, recent surgery, trauma, or infection. For instance, D-dimer levels may rise in patients with COVID-19 infection. COVID-19 is a highly contagious disease caused by SARS-CoV-2 virus, a type of human coronavirus predominantly affecting the respiratory tract. Although the exact mechanism remains unknown, high D-dimer levels have been associated with more severe disease and a higher mortality rate.  

Disorders like heart diseases and rheumatoid arthritis may also lead to positive D-dimer test results. Therefore, it is important for healthcare providers to correlate laboratory findings with the overall clinical picture.  

Once elevated D-dimer levels are detected, further diagnostic work-up is performed to uncover and treat the underlying condition.  

If a DVT is suspected, a Doppler ultrasound (a noninvasive imaging technique using sound waves to assess blood flow) or a venography (an X-ray of a vein after injection of a radiopaque dye) of the lower and upper limbs can be performed to confirm the diagnosis. Treatment of a confirmed DVT includes anticoagulants, or blood thinners, such as heparin, warfarin, and direct oral anticoagulants (DOACs) to prevent further formation of blood clots.  

If a PE is suspected, a chest CT angiography and ventilation-perfusion (V/Q) scan can be used to confirm its diagnosis. Depending on the severity, a PE can be treated with anticoagulants, thrombolytics (medications that dissolve blood clots, e.g., tissue plasminogen activator [tPA]), or embolectomy (i.e., surgical or catheter-based removal of the embolus). 

Diagnosis of DIC requires various laboratory tests, including a complete blood count (CBC) to assess the individual’s platelet count, tests to measure the concentration of clotting factors, and coagulation assays to observe how quickly the blood clots. Definitive treatment of DIC involves addressing the underlying cause. Supportive care may include blood products transfusions to replace blood components, anticoagulants to oppose excessive clotting, as well as IV fluids. 

Ischemic stroke is diagnosed with a brain CT scan or MRI, and once confirmed, treatment includes thrombolysis or thrombectomy. 

If COVID-19 is suspected, diagnosis begins with a history considering possible exposure, signs and symptoms, and physical assessment, followed by laboratory tests to confirm the diagnosis. Since there is no cure for COVID-19, treatment involves supportive therapy, including rest, hydration, and over-the-counter medications like paracetamol to reduce the fever and congestion.