D-Dimer

When blood clots form, the coagulation cascade converts fibrinogen into fibrin monomers, which polymerize and are stabilized by factor XIII through cross-linking. When these cross-linked fibrin clots are subsequently broken down by the enzyme plasmin (a process called fibrinolysis), the result is a series of degradation products, the most clinically important of which is D-dimer. The "D" in D-dimer refers to the D-domain of fibrin, and the term "dimer" indicates that two D-domains from adjacent fibrin strands remain linked together after plasmin cleavage. Because D-dimer can only be produced from cross-linked (not unlinked) fibrin, its presence specifically indicates that a fully formed clot has been made and is being broken down.

D-dimer's clinical utility stems from its very high sensitivity and high negative predictive value for thromboembolic events. A normal D-dimer level, combined with a low clinical probability score (using tools like the Wells score or Geneva score), effectively rules out pulmonary embolism (PE) and deep vein thrombosis (DVT) without the need for imaging. However, D-dimer is not specific for pathological thrombosis — levels can be elevated by surgery, trauma, infection, malignancy, pregnancy, inflammation, and aging, limiting its positive predictive value. Age-adjusted D-dimer cutoffs (using patient age multiplied by 10, in ng/mL for patients over 50) have been adopted to improve specificity in older adults.

D-dimer is measured using immunoassays that target the specific epitope created by factor XIII cross-linking and subsequent plasmin cleavage. Multiple assay formats exist, including ELISA, latex agglutination, and immunoturbidimetric methods, with quantitative assays preferred for their higher sensitivity. Results are typically reported in ng/mL or mg/L fibrinogen equivalent units (FEU), with standard cutoffs near 500 ng/mL FEU or 250 ng/mL D-dimer units (DDU).

Prevena Health is exploring whether continuous D-dimer monitoring may support earlier identification of thrombotic events in high-risk populations. Current D-dimer testing occurs only when a clinical suspicion of thromboembolism has already been raised — typically after symptoms like leg swelling, chest pain, or dyspnea have prompted an emergency department visit. Continuous surveillance aims to detect D-dimer elevations proactively, before symptoms reach thresholds that drive patients to seek care.

This approach may be particularly relevant for patients at elevated thrombotic risk, including post-surgical patients, individuals with cancer-associated hypercoagulability, and patients with inherited thrombophilia. By integrating continuous D-dimer trend data with other circulating biomarkers, Prevena's platform may support research into whether ambulatory coagulation monitoring can improve clinical outcomes for patients at risk of venous thromboembolism.