An elevated D-dimer test often prompts questions about what it signifies for one’s health. This test measures D-dimer, a small protein fragment that is not normally present in blood plasma unless the body’s coagulation system has been activated. This substance is created when a blood clot dissolves through a process called fibrinolysis.
The body forms a clot to stop bleeding from an injury, using a protein called fibrin to create a mesh. Once healing occurs, the clot is broken down, releasing fibrin degradation products, including D-dimer fragments. A high D-dimer level suggests significant formation and breakdown of blood clots has occurred somewhere in the body.
What an Elevated D-Dimer Test Indicates
The primary clinical use of a D-dimer test is to help rule out the presence of a harmful blood clot. Its value lies in its high sensitivity, meaning the test is very good at detecting the substance if it is present. If a person has a low or moderate assessed risk for a blood clot and their D-dimer result is normal, a doctor can be confident that a thrombotic event is not occurring, which helps avoid unnecessary testing.
Conversely, the test has low specificity, which means an elevated result is not definitive for a diagnosis. Many different situations, not just dangerous blood clots, can cause D-dimer levels to rise. A positive result does not confirm a clotting disorder but signals that further investigation is needed to determine the underlying cause.
Medical Conditions Associated with High D-Dimer Levels
An elevated D-dimer result prompts physicians to consider a range of possibilities, which can be grouped into clot-related and non-clot-related conditions. The most common clot-related concerns are venous thromboembolism (VTE), which includes deep vein thrombosis (DVT) and pulmonary embolism (PE). A DVT is a clot that forms in a deep vein, usually in the leg, causing pain and swelling.
A PE occurs if a piece of that clot breaks off and travels to the lungs, which can cause chest pain and difficulty breathing. Another serious condition is disseminated intravascular coagulation (DIC), a widespread activation of clotting throughout the body that can lead to multiple organ failure.
Numerous other factors unrelated to acute clots can also raise D-dimer levels. These include:
- Pregnancy
- Recent major surgery or physical trauma
- Infections like pneumonia or sepsis
- Various cancers
- Heart failure
- Autoimmune disorders
- Advanced age
The Diagnostic Process After an Elevated Result
The first step a physician takes after an elevated result is to assess the patient’s clinical pre-test probability by evaluating their individual risk factors and symptoms. This is often done using a structured scoring system, such as the Wells score, which helps categorize a person’s risk for DVT or PE as low, moderate, or high.
If the D-dimer is high and the clinical probability score suggests a clot is likely, the next step is imaging. The specific imaging test ordered depends on the suspected location of the clot. For a suspected DVT in the leg, a compression ultrasound is the standard method used to visualize the veins and identify any blockages. This non-invasive test uses sound waves to create images of blood flow.
When a pulmonary embolism is the concern, a computed tomography pulmonary angiography (CTPA) scan is most often used. This procedure involves injecting a contrast dye into the bloodstream and then using a CT scanner to get detailed images of the arteries in the lungs. In cases where a patient cannot receive contrast dye, such as due to a severe allergy or kidney problems, a ventilation-perfusion (V/Q) scan may be used as an alternative.
Interpreting D-Dimer Levels in Context
There is no single universal standard for what constitutes a “normal” D-dimer level, as reference ranges can vary between laboratories. A result below 500 ng/mL is considered negative, but this is not a rigid rule, and the specific units used can also differ.
D-dimer levels are known to increase naturally as people get older. To account for this and improve the test’s accuracy in older populations, many healthcare systems use an age-adjusted cutoff for patients over 50. This is often calculated with a simple formula: the patient’s age multiplied by 10 ng/mL. Using this age-adjusted value helps reduce the number of false positives in older adults.
A physician interprets a D-dimer level within the complete clinical picture. For example, a slightly elevated result in an older patient with no symptoms may be less concerning than the same result in a younger person who has signs of a DVT.