D-dimers in atrial fibrillation: a further step in risk stratification of thrombo-embolism?

Plasma fibrin D-dimers (hereafter D-dimers) are generated when the endogenous fibrinolytic system degrades fibrin, as in venous thrombo-embolism (VTE) and they consist of two identical subunits derived from two fibrin molecules. Unlike fibrinogen degradation products, which are derived from fibrinogen and fibrin, D-dimers are a specific crosslinked fibrin derivative. Because 2–3% of plasma fibrinogen is degraded to fibrin, small amounts are detectable in the plasma of healthy individuals. D-dimer levels may be increased in any condition involving the formation and degradation of fibrin, such as VTE, pulmonary embolism, infections, cancer, surgery, cardiac or renal failure, acute coronary syndromes, acute non-lacunar stroke, pregnancy, and sickle cell crises. D-dimer levels increase linearly with age. The classic microplate enzyme-linked immunosorbent assay (ELISA) technique is considered the gold standard but it is not used as a routine emergency test. Fully automated techniques have been developed, such as the VIDAS test (ELISA method with a final detection in fluorescence), but also immunofiltration (membrane ELISA) techniques and instantaneous methods which allow a diagnosis within a few minutes at the expense of a semiquantitative approach.