When it comes to thrombosis, one of the diagnostic methods is measuring the level of D-dimer in the blood, as one of the many markers used in medicine. However, before discussing the role of D-dimer in diagnosing thrombosis in more detail, we should first explain what D-dimer is and how a thrombus (blood clot) forms.
What is D-dimer?
In simple terms, D-dimer is a protein fragment released during the breakdown of a blood clot.
How is D-dimer formed?
When a blood vessel or tissue is injured and bleeding, the body initiates a process called hemostasis, which forms a blood clot to limit blood loss and eventually stop the bleeding. During this process, fibrin protein threads are formed, creating a fibrin network that helps build a blood clot where it’s needed (at the site of the injury). After the injury heals and the bleeding stops, the body produces an enzyme called plasmin. This enzyme breaks down the blood clot, as it is no longer needed. Plasmin breaks the clot into smaller fragments that are eliminated from the body. D-dimer is one of these fragments, and for this reason, it is considered a good indicator of the presence of thrombosis in the body. In healthy individuals, D-dimer values are low or even below the detection limit of the test (undetectable value).Can D-dimer levels be elevated without thrombosis?
Yes, it is possible. Slightly elevated D-dimer levels are not always a definite sign of thrombosis, as they can increase during various inflammatory processes in the body. Therefore, it is important to interpret D-dimer test results along with other clinical parameters to determine the exact cause of the elevated values. In addition to acute inflammatory processes, D-dimer levels may also be elevated in certain traumas, during pregnancy (where different reference values apply), due to smoking, or in malignant diseases. In practice, slightly elevated D-dimer levels are most commonly seen as a result of some acute inflammatory process and in pregnant women.
When should a D-dimer test be done?
Doctors usually recommend a D-dimer test when symptoms of blood clotting are present, which can lead to serious conditions such as:
- Deep vein thrombosis (DVT) – formation of clots in deep veins, most commonly in the legs.
- Pulmonary embolism (PE) – when a blood clot reaches the lungs and blocks a pulmonary artery.
- Disseminated intravascular coagulation (DIC) – a serious condition where blood clots form throughout the body due to excessive activation and consumption of clotting factors.
- Stroke (heart, brain)
Some of the symptoms that indicate the need for a D-dimer test include:
- Intense pain and/or swelling in the limbs (arms, legs)
- Redness and temperature changes in the limbs
- Chest pain
- Coughing up blood
- Difficulty breathing and coughing
It is always recommended to consult a doctor if you experience any of these symptoms. The attending physician will take the necessary steps to establish an accurate and timely diagnosis.
Reference values for D-dimer
There are various tests available on the market, with different technologies and two main types of reagents: D-dimer units (DDU) or fibrinogen equivalent units (FEU). It should be noted that there is variability in the units in which the results are expressed. This has caused much confusion, especially when the D-dimer test became significant in COVID testing panels. Therefore, to maintain measurement traceability, it is recommended that tests are performed using the same technique (same test, same units). In the Biodiagnostica laboratory, the D-dimer test is performed on the Siemens Immulite 2000 apparatus, and the recommended reference range is:
| Test | Reference Values |
|---|---|
| D-dimer | <0.5 mg/l |
D-dimer Reference Values in Pregnancy *
| First trimester | 0.05 – 0.95 |
| Second trimester | 0.32 – 1.29 |
| Third trimester | 0.13 – 1.70 |
* Abbassi-Ghanavati M, Greer LG, Cunningham FG. A reference table of normal laboratory values in uncomplicated pregnancies. In: Cunningham FG, Leveno KJ, Bloom S, Hauth JC, Rouse DJ, Spong CY (eds). Williams Obstetrics. 23th Edition. New York NY: McGraw–Hill, 2010;1259-64
Conclusion
D-dimer is a useful marker for diagnosing thrombosis. Its role is to identify the presence of a clot or an inflammatory process in the body. Determining D-dimer levels can greatly assist doctors in making an accurate diagnosis, monitoring treatment effectiveness, and assessing the risk of thrombosis in certain patients. Therefore, D-dimer testing plays a vital role in maintaining health and preventing serious complications related to thrombosis.
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