D-Dimer Formation and Characteristics

Biochemical Formation Process

D-dimer is generated through plasmin-mediated proteolysis of crosslinked fibrin during fibrinolysis, representing the smallest fragment that is only produced when crosslinked fibrin is digested 1
The formation occurs through a sequential process, including initial coagulation activation, where fibrinogen is converted to fibrin monomers, which polymerize to create fibrin strands 2
Crosslinking occurs through Factor XIIIa, which covalently crosslinks adjacent fibrin monomers at their D-domains, creating a stable fibrin mesh 2
Fibrinolysis occurs through plasmin, which cleaves the crosslinked fibrin, releasing various fibrin degradation products (FDPs) 1
D-dimer generation specifically refers to the covalently bound D-domains of adjacent fibrin monomers along with an E-domain of the opposite and staggered strand 2

D-dimer has a relatively long half-life of approximately 16 hours in circulating plasma 1
The long half-life of D-dimer obfuscates accurate interpretation of single time-point measurements, requiring sequential measurements to confirm active fibrinolysis 1

Monoclonal antibodies used in D-dimer assays are specific for epitopes on D-D fragments and are absent on fibrinogen and non-crosslinked fibrin fragments, ensuring the test specifically detects crosslinked fibrin breakdown rather than simple fibrinogen degradation 3
Not all fibrin degradation products are D-dimers, as FDPs can be generated from plasmin-mediated proteolysis of both fibrinogen and fibrin, but D-dimer specifically requires crosslinked fibrin 1
Fragments released from proteolysis of fibrinogen and fibrin by elastase and other enzymes in circulation can interfere with D-dimer testing but are not true D-dimers 3