D-dimer – a test used in combination with other laboratory and instrumental (imaging, non-laboratory) tests to exclude the diagnoses of deep vein thrombosis, pulmonary embolism, stroke. It can be used to diagnose other diseases or disorders that make the blood prone to clotting. It is also designed to diagnose disseminated intravascular coagulation (DIC) and to monitor the effectiveness of treatment for DIC syndrome.
When should I be tested?
D-dimer testing should be performed in people with symptoms of deep vein thrombosis, such as:
1. pain or tenderness, usually in one leg or part of one leg;
2. swelling, swelling of the limb;
3. discolouration of the skin of the extremities.
The test can be given to people with symptoms of pulmonary embolism such as:
1. shortness of breath, difficulty breathing;
2. coughing, expectoration of blood;
3. chest pain;
4. increased heart rate.
D-dimers are a useful test when your doctor suspects diseases other than pulmonary embolism or thrombosis, which can cause similar symptoms (for example, COVID caused by SARS-Cov-2 virus).
People with symptoms of DIC syndrome (bleeding gums, nausea, vomiting, severe muscle and abdominal pain, seizures and reduced urine output) should have other laboratory tests in addition to the D-dimer test, such as PL, ADTL, fibrinogen and platelet counts (as part of a general haematology test), to help in the diagnosis of DIC syndrome. D-dimer testing should also be performed in patients with DIC undergoing treatment to monitor treatment.
What sample is needed for the test?
Blood is drawn from a vein in the arm.
How to prepare for the survey?
There is no special preparation.
What do my results mean?
The results of the d-dimer test can be expressed in d-dimer units (DDU) or fibrinogen equivalent units (FEU). Depending on the expression of the results (DDU or FEU), please consult the laboratory that performed the test on the correct way to interpret the results.
A normal or negative D-dimer result (in FEU units <500 µg/l) means that there is a high probability of not having an acute blood clotting condition (DIC syndrome) or a disease that can lead to the formation and subsequent disintegration of blood clots. A negative D-dimer test result is considered the most reliable and useful when the test is performed in a person at low risk of thromboembolism. The test is useful for ruling out bleeding disorders as a cause of the symptoms observed.
A positive D-dimer test result (FEU ≥500 µg/l) indicates an abnormally high level of fibrin breakdown products in the body. This means that blood clots have formed and broken down, but it is not clear where they are and why.
However, a positive D-dimer result does not necessarily indicate thrombosis, as the concentration may be elevated for other reasons, such as after a recent surgery, trauma, infection, myocardial infarction, certain cancers and liver disease. In addition, D-dimer levels tend to increase with age, and increase during pregnancy.
In people being treated with anticoagulants, or other drugs that affect the clotting system, a decrease in D-dimer levels is a sign of successful treatment, and conversely, an increase is a sign of ineffective treatment.
Related studies
Prothrombin time, ADTL, fibrinogen, platelet count, general haematology
Related conditions/diseases.
Deep vein thrombosis, pulmonary embolism, DIC syndrome, sepsis, infections.
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