Ddimers

D-dimers are fibrin degradation products formed when plasmin cleaves cross-linked fibrin during the breakdown of clots. Their presence in the blood indicates recent or ongoing coagulation and fibrinolysis, reflecting activity within the hemostatic system. The term is commonly used in the plural form, D-dimers, in clinical practice.

In medicine, D-dimer testing is primarily used to help exclude venous thromboembolism (deep vein thrombosis and pulmonary embolism) in patients with low to intermediate pretest probability. A negative result can effectively rule out thrombosis in such patients and may reduce the need for additional imaging. A positive result, however, is nonspecific and can be elevated in a variety of conditions beyond thrombosis, including infection, inflammation, liver disease, cancer, pregnancy, recent surgery or trauma, aging, and other states of systemic activation.

Testing and interpretation: D-dimer is measured by immunoassays. Many laboratories report results in fibrinogen-equivalent units (FEU) or D-dimer units (D-DU). High-sensitivity D-dimer assays are commonly used, and interpretation depends on pretest probability. Age-adjusted thresholds (for patients over 50) are often employed, using age in years multiplied by 10 ng/mL FEU. A result above the cutoff prompts further evaluation rather than a definitive diagnosis.

Limitations: The test lacks specificity for thrombosis and can be elevated in numerous non-thrombotic conditions, leading to false positives. Conversely, a negative result helps rule out disease only in low to intermediate-risk patients; false negatives can occur in very early thrombosis or with certain assay types. Therefore, D-dimer results are interpreted in the context of clinical assessment and, when needed, in combination with imaging studies.

Other uses include assessing recurrence risk after stopping anticoagulation in some settings, though D-dimer is not routinely used to monitor therapy.