D dimer
When fibrin fibers are cleaved, fragments are formed-D-dimers. When determining the content of D-dimers with the help of specific antisera, one can judge to what extent fibrinolysis, but not fibrogenolysis, is expressed in the test blood.
The reference values (norm) of the concentration of D-dimer in blood plasma are less than 0.25 μg / ml (250 μg / l) or 0.5 μg fibrinogen equivalents / ml (500 μg fibrinogen equivalents / liter).
Determination of D-dimer in plasma is used to exclude thrombosis of any localization and diagnosis of DIC syndrome. In pulmonary embolism, the D-dimer content in the plasma usually exceeds 0.5 μg / ml (500 μg / l).
The reasons for increasing the D-dimer
The increased content of D-dimer is one of the main markers of activation of the hemostasis system, since it reflects both the formation of fibrin in the blood under study, and its lysis. The period of deducing the D-dimer from the bloodstream is 6 hours, which is significantly higher than other markers of activation of the coagulation cascade (fragment 1 + 2 - prothrombin proteolysis product, thrombin-antithrombin complex, fibrinopeptide A). In connection with this, blood plasma samples can not be stored for more than 6 hours.
Elevated concentrations of D-dimer in blood plasma can be with IHD, myocardial infarction, malignant tumors, liver diseases, active inflammatory process, infectious diseases, extensive hematomas, thrombolytic therapy, pregnancy, in people over 80 years old.
The introduction of heparin causes a sharp and immediate drop in the concentration of D-dimer in the plasma, which continues more slowly and later in the treatment of direct anticoagulants. The appointment of indirect anticoagulants is also accompanied by a decrease in the content of D-dimer, but it is more smooth. Usually, in the context of treatment with indirect anticoagulants, the D-dimer concentration below 500 μg / l is reached after 3 months.
In patients with a deficiency of tissue plasminogen activator or high activity of plasminogen activator inhibitor (which leads to a decrease in fibrinolytic activity of blood plasma), the concentration of D-dimer may not increase even in the presence of deep vein thrombosis or pulmonary embolism.
In patients with myocardial infarction and obliterating atherosclerosis of the vessels of the lower limbs, the increased concentration of D-dimer in the blood plasma is associated with an increase in the likelihood of complications. The increase in the level of D-dimer and fibrinogen in patients with a constant form of atrial fibrillation is considered a harbinger of thromboembolic complications.
Infections, inflammatory processes, hemorrhagic complications, the presence of rheumatoid factor in the blood, the formation of fibrin in the healing of postoperative wounds can be accompanied by an increase in the concentration of the D-dimer.
The diagnostic sensitivity of determining the D-dimer for the diagnosis of pulmonary artery thromboembolism is 90%, the specificity is less than 50%, for diagnosis of deep vein thrombosis 60-100% and 29-91%, respectively.
The concentration of D-dimer in the blood plasma increases in the early stages of pregnancy, reaching its end 3-4 times higher than the original. Significantly higher concentrations of D-dimer are detected in women with complications of pregnancy (gestosis, pre-eclampsia), as well as in pregnant women with diabetes mellitus and kidney disease.
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