D-Dimer is a protein fragment formed during the dissolution of a blood clot, the level of which in the blood plasma reflects the activity of the processes of thrombosis and fibrinolysis. D-dimer test is used as an auxiliary test, and the diagnosis is determined taking into account the clinical signs and the results of a comprehensive examination. This study is prescribed for the purpose of diagnosing DIC syndrome or monitoring the treatment of thrombosis with anticoagulants. Plasma isolated from venous blood is used for analysis. The determination of the D-dimer is included in the study of the coagulogram (a set of blood parameters regulating the clotting process). In a healthy adult, the D-dimer level ranges from 0 to 0.55 micrograms FEU/ml. Readiness of the results of the study: 1 day.
D-dimer is a protein fragment formed as a result of the breakdown of fibrin under the influence of plasmin. When a vessel is damaged, the body triggers the blood clotting process in response. This leads to the formation of blood clots consisting of fibrin, thanks to which the blood clot is retained in the place where it was formed. Blood clots sometimes form not only on the outside of damaged vessels, but also in their inner part. This process occurs due to damage to the internal vascular wall or changes in local hemodynamics (for example, stagnation of blood). The concentration of D-dimer is directly proportional to the level of fibrin and the activity of fibrinolysis, so the analysis helps to determine at what stage the process of thrombosis is.
D-dimer test in the blood is often used in emergency departments. So, in cardiology and vascular surgery, the analysis is carried out to assess the risk of arterial thrombosis, PE, deep vein thrombosis. It has been proven that in patients with coronary heart disease, the level of D-dimer in the blood increases, which can subsequently lead to complications in the form of a disturbed rhythm or cardiogenic shock. Also, the D-dimer assay is often used in surgery to assess the state of the blood coagulation system before surgery.
Indications for the analysis
Indications for d-dimer test are pathological processes and conditions in which the risk of thrombosis in the vessels increases: atrial fibrillation, varicose veins of the legs, complications after infectious diseases, diseases of the cardiovascular system or surgical interventions. Doctors may prescribe a study on the concentration of D-dimer during pregnancy or taking oral contraceptives, when the risk of blood clots in the vessels also increases. With thrombosis, the body triggers processes that lead to the destruction of clots. As a result, fibrin is destroyed under the influence of plasmin, and D-dimers are formed.
Also, the study is prescribed to determine the tactics of treatment and prediction of acute thrombosis with a fatal outcome. For each pathology, for the correct interpretation of the results obtained, it is important to evaluate the content of D-dimer in the blood precisely in dynamics. An analysis to determine the level of D-dimer is also indicated for monitoring the effectiveness of taking medications in the case of thrombolytic or anticoagulant therapy.
The main advantage of the test for determining the presence of D-dimer in the blood is its high negative prognostic significance – 98% (if the analysis indicator is within the reference values, then thrombosis is practically excluded). Thanks to these diagnostic capabilities, it is possible to identify such a serious pathology as pulmonary embolism.
Preparation and collection of material
Blood plasma is used for the study. If necessary, the biomaterial is transported or stored in a vacuum container with sodium citrate. It is forbidden to store blood plasma samples for more than 5-6 hours, since the D-dimer elimination period is about 6 hours. It is preferable to take the analysis in the morning. Before taking blood, the patient is prohibited from eating or drinking sugary and carbonated drinks. It is important to limit physical activity and avoid stress. 10-11 hours before the analysis, it is necessary to exclude the intake of alcoholic beverages and smoking. Before taking blood, you can drink only non-carbonated water. It is recommended to exclude taking medications. If it is impossible to interrupt the course of treatment, it is important to warn the laboratory assistant about this. The biomaterial should be taken before other studies (X-ray, ultrasound).
Three methods are used to diagnose the D-dimer content: microlatex agglutination, ELISA and immunochromatography. Immunoturbidimetry (microlatex agglutination) is most widely used in laboratories. The principle of the technique: the patient’s plasma containing a D-dimer is added to the reagent, after which its optical density increases. The reagent forms a suspension of latex particles that are coated with antibodies against the D-dimer. At the same time, the measured increase in optical density is proportional to the level of the D-dimer in the biomaterial. The analysis is performed within one day.
The main problem of the study is the complete lack of standardization not only at the stage of equipment production, but also in the manufacture of reagents, control materials or calibrators of test systems. Moreover, the concentration of D-dimer can be determined in units of two types: DDU and FEU, which also complicates the interpretation of the analysis results by the attending physician. The reference values of the D-dimer are from 0 to 0.55 micrograms FEU/ml. Also, the concentration can be indicated in a dimer-equivalent unit of DDU or mg/l. In this case, the norm is 0.25 mg/l.
Raising the level
The causes of increased D-dimer in the blood are DIC syndrome, hepatic or renal insufficiency, as well as venous thrombosis. Especially dangerous is the DIC syndrome, in which all the vessels are clogged with small blood clots. This pathology often leads to death. The physiological reason for the increase in D-dimer in the blood is pregnancy. During gestation, there may be slight increases in the indicator (up to 1.5 micrograms / ml) due to the activation of the coagulation system, which is a variant of the norm. But the very high concentration of D-dimer observed in gestosis and preeclampsia requires more serious attention and drug therapy.
In the elderly (in patients over 80 years of age), with rheumatoid arthritis and infectious diseases, an increase in the D-dimer occurs without the formation of blood clots in the body. For proper diagnosis, it is important to additionally take tests for other indicators (for example, UAC, fibrinogen, thrombin time, APTT, rheumatoid factor). The concentration of D-dimer in the bloodstream is influenced by the size of the thrombus, the time from its occurrence to the appointment of anticoagulants, taking medications that lower the level of D-dimer, and thrombolytic treatment.
Lowering the level
The reasons for the decrease in D-dimer in the blood in the presence of obvious signs of pathology are a very small thrombus, reduced fibrinolytic activity or increased concentration of a plasminogen activator inhibitor. In some cases, the reason for the decrease in the D-dimer in the blood is technological problems at the preanalytical level. With a marked decrease in the indicator during pregnancy, there is a possibility of blood clotting disorders. In this case, a woman in labor may experience bleeding during delivery, sometimes leading to death.
Treatment of abnormalities
Basically, the D-dimer test is used as an auxiliary test, and treatment is prescribed, additionally taking into account the clinical symptoms and the results of other tests. In case of deviations from the norm, it is important to normalize the drinking regime, increase physical activity (move more). With the results of the analysis, it is necessary to contact a phlebologist, surgeon, therapist, cardiologist, infectious disease specialist or hematologist. The attending physician will prescribe adequate treatment to normalize all blood parameters.