D-dimer

Structure of D-dimer

D-dimer is a fibrin degradation product (or FDP), a small protein fragment present in the blood after a blood clot is degraded by fibrinolysis. It is named because it contains two D fragments of the fibrin protein joined by a cross-link. D-dimer concentration may be determined by a blood test to help diagnose thrombosis.

Clinical significance

D-dimer is a significant marker in the diagnosis of thrombotic disorders. It is used primarily to exclude the presence of an inappropriate blood clot (thrombus). A negative D-dimer test indicates that it is highly unlikely that a thrombus is present. Conversely, a positive D-dimer test is not specific and does not confirm the presence of a thrombus, as D-dimer levels can be elevated in other conditions such as inflammation, infection, or liver disease.

Diagnostic use

The D-dimer test is commonly used in the diagnosis of deep vein thrombosis (DVT), pulmonary embolism (PE), and disseminated intravascular coagulation (DIC). It is particularly useful in emergency settings to rule out thromboembolic events in patients with low to moderate risk.

Pathophysiology

D-dimer is formed by the action of plasmin on cross-linked fibrin. When a blood clot is formed, the coagulation cascade is activated, leading to the conversion of fibrinogen to fibrin. Fibrin forms a mesh that stabilizes the clot. Plasmin, an enzyme, breaks down the fibrin mesh, resulting in the release of D-dimer into the bloodstream.

Testing

D-dimer levels are measured using a blood test. The test is often performed using an enzyme-linked immunosorbent assay (ELISA) or a latex agglutination test. The results are typically reported in fibrinogen equivalent units (FEU) or D-dimer units (DDU).

Limitations

While the D-dimer test is a useful tool for ruling out thrombotic events, it has limitations. Elevated D-dimer levels can occur in a variety of conditions, including pregnancy, trauma, surgery, and cancer. Therefore, a positive D-dimer test must be interpreted in the context of the patient's clinical presentation and risk factors.

Related pages

• Thrombosis
• Fibrinolysis
• Coagulation
• Pulmonary embolism
• Deep vein thrombosis