Also Known As: Fragment D-dimer // Fibrin Degradation Fragment
A D-dimer test is most often used to find out whether you have a blood clotting disorder. These disorders include:
- Deep vein thrombosis (DVT), a blood clot that's deep inside a vein. These clots usually affect the lower legs, but they can also happen in other parts of the body.
Symptoms of DVT include:
- Leg pain or tenderness
- Leg swelling
- Redness or red streaks on the legs
- Pulmonary embolism (PE), a blockage in an artery in the lungs. It usually happens when a blood clot in another part of the body breaks loose and travels to the lungs. DVT clots are a common cause of PE.
Symptoms of PE include:
- Trouble breathing
- Chest pain
- Rapid heartbeat
- Disseminated intravascular coagulation (DIC), a condition that causes too many blood clots to form. They can form throughout the body, causing organ damage and other serious complications. DIC may be caused by traumatic injuries or certain types of infections or cancer.
- Stroke, a blockage in the blood supply to the brain.
What is D-Dimer?
D-Dimer is one of the protein fragments produced when a blood clot gets dissolved in the body. It is normally undetectable or detectable at a very low level unless the body is forming and breaking down blood clots. Then, its level in the blood can significantly rise. A D-dimer test is a blood test that can be used to help rule out the presence of a serious blood clot.
What is hemostasis and blood clots?
When a blood vessel or tissue is injured and begins to bleed, a process called hemostasis is initiated by the body to create a blood clot to limit and eventually stop the bleeding. This process produces threads of a protein called fibrin, which link together to form a fibrin net. That net, together with platelets, helps hold the forming blood clot in place at the site of the injury until it heals.
What is plasmin?
Once the area has had time to heal and the clot is no longer needed, the body uses an enzyme called plasmin to break the clot (thrombus) into small pieces so that it can be removed. The fragments of the disintegrating fibrin in the clot are called fibrin degradation products (FDP), which consist of variously sized pieces of crosslinked fibrin. One of the final fibrin degradation products produced is D-Dimer, which can be measured in a blood sample when present. Normally, with a little time, D-dimer goes away. But you can get high levels of D-dimer in your blood if you have a major clot like with deep vein thrombosis (DVT). With DVT, you have a clot deep in one of your veins, usually in your legs, and it can lead to serious problems.
When can D-Dimer levels rise?
The level of D-Dimer in the blood can significantly rise when there is significant formation and breakdown of fibrin clots in the body.
However, a positive D-Dimer test cannot predict whether or not a clot is present. It indicates that further diagnostic procedures are required (e.g., ultrasound, CT angiography).
Factors associated with inappropriate blood clot formation:
There are several factors and conditions associated with inappropriate blood clot formation. One of the most common is deep vein thrombosis (DVT), which involves clot formation in veins deep within the body, most frequently in the lower legs. These clots may grow very large and block blood flow in the legs, causing swelling, pain, and tissue damage. It is possible for a piece of the clot to break off and travel to other parts of the body. This "embolus" can lodge in the lungs, causing a pulmonary embolus or embolism (PE). Pulmonary embolisms from DVT affect more than 300,000 people in the U.S. each year.
Where do clots form and why test for D-Dimer?
While clots most commonly form in the veins of the legs, they may also form in other areas as well. Measurements of D-Dimer can be used to help detect clots in any of these sites. For example, clots in coronary arteries are the cause of myocardial infarction (heart attacks). Clots may form on the lining of the heart or its valves, particularly when the heart is beating irregularly (atrial fibrillation) or when the valves are damaged. Clots can also form in large arteries as a result of narrowing and damage from atherosclerosis. Pieces of such clots may break off and cause an embolus that blocks an artery in another organ, such as the brain (causing a stroke) or the kidneys.
Normal levels: If your results show low or normal D-dimer levels in the blood, it means you probably don't have a clotting disorder.
If your results show higher than normal levels of D-Dimer, it may mean you have a clotting disorder. But it cannot show where the clot is located or what type of clotting disorder you have. Also, high D-Dimer levels are not always caused by clotting problems. Other conditions that can cause high D-Dimer levels include pregnancy, heart disease, and recent surgery. If your D-Dimer results were not normal, your provider will probably order more tests to make a diagnosis. This test can’t confirm that you have Deep vein thrombosis (DVT) or Pulmonary embolism (PE). It can only help rule them out.
Some of the other tests that your provider might order include:
- Doppler ultrasound, a test that uses sound waves to create images of your veins.
- CT angiography. In this test, you are injected with a special dye that helps your blood vessels show up on a special type of x-ray machine.
- Ventilation-perfusion (V/Q) scan. These are two tests that may be done separately or together. They both use small amounts of radioactive substances to help a scanning machine see how well air and blood move through your lungs.
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