The D-dimer is a fibrin degradation product and corresponds to the in vivo formation and degradation of a fibrin clot. Since 2% to 3% of plasma fibrinogen is physiologically converted to cross-linked fibrin and then degraded, small amounts of D-dimer are normally present in the plasma of healthy individuals. But when the coagulation and fibrinolytic cascades are activated in vivo, the plasma concentration of D-dimer increases dramatically. The converse is also true: plasma D-dimer concentration decreases in response to anticoagulant therapy and the resolution of symptoms. The protein has a plasma half-life of approximately 8 hours and clearance occurs mainly via the kidneys and reticulo-endothelial system.
