D-dimer levels are measured by latex immunoassay which employs latex particles coated with antibodies to D-dimers to capture D-dimers in the test plasma. The D-dimers act as a bridge between latex particles that leads to a degree of agglutination directly proportional to concentration, which is measured turbidimetrically.
Progressive degradation of cross-linked fibrin by plasmin leads to formation of small terminal derivates, one of which is D-dimer. Each D-fragment in a D-dimer molecule is derived from a different parent fibrin(ogen) molecule and remain joined due to cross-linking, so detection of D-dimers in plasma indicates the presence of a blood clot. Elevated D-dimers are a marker of reactive fibrinolysis and can be encountered in conditions such as DVT, PE & DIC. A normal D-dimer level has a high negative predictive value for DVT & PE.