D-Dimer

The D-dimer test is used alongside a non-high clinical pretest probability to help rule out deep vein thrombosis and pulmonary embolism; a result below the established cutoff in this setting can avert additional venous thromboembolism testing. The assay also supports evaluation for disseminated intravascular coagulation. As a measurement of a fibrin degradation fragment, D-dimer serves as an adjunct for gauging thrombus formation and for tracking anticoagulant therapy in thromboembolic disease, with interpretation integrated with clinical findings and other laboratory data.

D-dimer is released when plasmin degrades cross-linked fibrin within a thrombus, providing a readout of both coagulation and fibrinolytic system activity. Its concentration reflects fibrinolytic activity and, indirectly, the magnitude of thrombin generation. Thrombosis may result from endothelial injury, blood flow stasis, or abnormal shear stress and is observed with conditions such as postoperative states, infection, and venous insufficiency. Physiologic increases occur during pregnancy, most prominently in the third trimester; available studies have not shown a consistent link between D-dimer concentration and adverse pregnancy outcomes. Elevated values are common among hospitalized patients and in numerous nonthrombotic conditions, limiting specificity. D-dimer is a supportive test that requires interpretation in the context of the clinical presentation and complementary laboratory results. Normal concentrations can be seen with subsegmental or peripheral pulmonary embolism, distal deep vein thrombosis, or when sampling is delayed after thrombus formation due to clearance of the fibrin degradation fragment. Use of D-dimer to exclude pulmonary embolism in patients with high pretest probability has not been established.