The D-dimer test is a blood test that helps detect the presence of abnormal blood clots in the body. It measures a protein fragment called D-dimer, which is released when a blood clot dissolves.
Doctors usually order a D-dimer test to help rule out serious conditions like deep vein thrombosis (DVT), pulmonary embolism (PE), or disseminated intravascular coagulation (DIC). The test is quick, non-invasive, and plays an important role in identifying problems related to how the blood clots and breaks down.
Treatment depends on the underlying cause of abnormal results. If the D-dimer test is high, a doctor may order other tests to confirm or rule out clotting disorders and begin treatment with medications, such as anticoagulants, to prevent complications like stroke or pulmonary embolism.
Why it's done
The D-dimer test is normally ordered by the doctor to rule out the possibility of deep vein thrombosis (DVT) or pulmonary thromboembolism (PTE). This marker is typically increased in these situations.
However, because it is a coagulation marker, the D-dimer test can also be ordered to evaluate the coagulation cascade or how blood clots form. It is also used in the diagnosis or monitoring of disseminated intravascular coagulation (DIC), stroke, and other conditions that interfere with coagulation, such as heart problems, cancer, or inflammation.
Doctors may also use the D-dimer test as part of diagnostic algorithms like the Wells score or the YEARS criteria to safely exclude venous thromboembolism in patients with low or intermediate risk.
How it's done
The D-dimer test is performed on a blood sample collected in a blue-top tube containing sodium citrate anticoagulant. The tube must be filled to at least 90% capacity to maintain the proper blood-to-anticoagulant ratio, and the sample should be gently inverted several times after collection. Whole blood is stable at room temperature for about 4 hours and plasma for up to 24 hours when refrigerated.
Most laboratories use immunoturbidimetric assays, which measure light scattering from latex particles coated with antibodies that bind D-dimer. Other laboratories may use ELISA-based methods, which were once considered the gold standard but are now largely replaced by faster, automated techniques.
Interpreting results
The reference value for adults is usually less than 500 ng/mL (0.5 µg/mL FEU). However, interpretation depends on the person’s health status and clinical context, and results must always be analyzed along with other tests like prothrombin time, INR, or fibrinogen level.
Mild elevation (500–1000 ng/mL)
A mild increase in D-dimer levels may occur after recent surgery, infection, pregnancy, or small clots that have dissolved naturally. These cases usually indicate temporary or mild activation of the clotting system.
Moderate elevation (1000–5000 ng/mL)
Moderately elevated results may suggest more serious conditions such as deep vein thrombosis, pulmonary embolism, advanced cancer, or severe inflammation. Further testing is often needed to determine the exact cause.
Marked elevation (>5000 ng/mL)
Significantly high D-dimer levels are typically seen in disseminated intravascular coagulation (DIC), large pulmonary embolisms, or severe systemic disease. These cases require urgent medical attention and management of the underlying condition.
Risks & limitations
The D-dimer test is very sensitive but not specific, and false positives are common. Elevated levels may occur without any actual blood clot, particularly in people who are older, pregnant, hospitalized, or have chronic inflammation, infection, trauma, or cancer.
False negatives can occur if the test is performed too early, before clots form, or if the patient is already receiving anticoagulant therapy. Inconsistent reference ranges between laboratories and differences in testing methods can also affect interpretation.
Special populations
The D-dimer test can be influenced by factors such as age, pregnancy, and certain health conditions, so interpretation may differ for specific groups of people.
1. Pregnancy
D-dimer levels increase naturally during pregnancy, reaching their highest levels in the third trimester. Standard adult cutoffs are not reliable, so trimester-specific or adapted algorithms are used. For example, the pregnancy-adapted YEARS algorithm applies a cutoff of 1000 ng/mL when no other high-risk clinical signs are present. This approach can reduce the need for imaging and unnecessary radiation exposure.
2. Older adults
Because D-dimer levels tend to rise with age, using age-adjusted thresholds improves diagnostic accuracy in people over 50 years. Studies show that applying the formula (age × 10 ng/mL) increases the proportion of elderly patients in whom VTE can be safely excluded while maintaining a high negative predictive value.
3. Children
Limited evidence suggests that normal D-dimer values vary by age, with higher ranges in newborns and decreasing toward adult levels in adolescence. Although the test can help rule out thromboembolism in low-risk older children, it should be interpreted cautiously because sensitivity and specificity differ from adults.
4. Cancer patients
In people with cancer, D-dimer levels are often elevated even without thrombosis. Very high values (above 5000–6000 ng/mL) may indicate an increased risk of venous thromboembolism and are also associated with tumor progression and poorer prognosis.