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D-dimer is a blood test performed in the medical laboratory to diagnose thrombosis. Since its introduction in the 1990s, it has become an important test performed in patients suspected of thrombotic disorders. While a negative result practically rules out thrombosis, a positive result can indicate thrombosis but does not rule out other potential etiologies. Its main use, therefore, is to exclude thromboembolic disease where the probability is low.
D-dimer testing is of clinical use when there is a suspicion of deep venous thrombosis (DVT) or pulmonary embolism (PE). In patients suspected of disseminated intravascular coagulation (DIC), D-dimers may aid in the diagnosis.
For DVT and PE, there are various scoring systems that are used to determine the a priori clinical probability of these diseases; the best-known were introduced by Wells et al (2003).
In some hospitals, they are measured by laboratories after a form is completed showing the probability score and only if the probability score is low or intermediate. This would reduce the need for unnecessary tests in those who are high-probability.
Most sampling kits have 0-300 ng/ml as normal range. Values exceeding 250, 300 or 500 ng/ml (different for various kits) are considered positive.
Types of assays
Fibrin degradation products (FDPs) are formed whenever fibrin is broken down by enzymes (e.g. plasmin). Determining FDPs is not considered useful, as this does not indicate whether the fibrin is part of a blood clot (or being generated as part of inflammation).
D-dimers are unique in that they are the breakdown products of a fibrin mesh that has been stabilized by Factor XIII. This factor crosslinks the E-element to two D-elements. This is the final step in the generation of a thrombus.
Plasmin is a fibrinolytic enzyme that organizes clots and breaks down the fibrin mesh. It cannot, however, break down the bonds between one E and two D units. The protein fragment thus left over is a D-dimer.
D-dimer assays rely on monoclonal antibodies to bind to this specific protein fragment. The first patented MoAb of the kind was D Dimer-3B6/22, although others have been developed.
Various kits have a 93-95% sensitivity and about 50% specificity in the diagnosis of thrombotic disease.
D-dimer testing was originally developed in the diagnosis of disseminated intravascular coagulation. In the 1990s, they turned out to be useful in diagnosing thromboembolic process.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "D-dimer". A list of authors is available in Wikipedia.|