What is a D-dimer test?

A D-dimer test looks for D-dimer in blood. D-dimer is a protein fragment (small piece) that's made when a blood clot dissolves in your body. D-dimer isn't usually found in your blood unless your body is making or breaking up blood clots.

A blood clot is a mass of blood that forms when platelets, proteins, and cells in the blood stick together. When you get hurt, your body forms a blood clot to stop the bleeding. Blood clotting is an important process that prevents you from losing too much blood when you are injured.

Normally, your body will dissolve the clot once your injury has healed. With a blood clotting disorder, clots can form when you don't have an injury, or they don't dissolve when they should. These disorders can be serious and even life-threatening.

Other names: fragment D-dimer, fibrin degradation fragment

What is it used for?

A D-dimer test is used to check if you may have a blood clot. The test helps to find out if you need more tests to check for blood clotting disorders. A D-dimer test may also be used to monitor how well treatments for a blood clotting disorder like disseminated intravascular coagulation (DIC) are working.

Blood clotting disorders that the D-dimer test may be used for include:

• Deep vein thrombosis (DVT), a blood clot that forms in a vein deep in your body. These clots usually affect the lower legs, but they can also happen in other parts of your body.
• Pulmonary embolism (PE), a blockage in a lung artery. It usually happens when a blood clot in another part of your body breaks loose and travels to your lungs. DVT clots are a common cause of PE.
• 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 health issues. DIC may be caused by inflammation, infection, or cancer.
• Stroke, which can happen when blood flow to a part of the brain is blocked.

Why do I need a D-dimer test?

You may need this test if you have symptoms of a blood clotting disorder, such as deep vein thrombosis (DVT) or a pulmonary embolism (PE).

Symptoms of DVT in your leg include:

• Leg pain or tenderness
• Leg swelling
• Redness or darkening of the skin on the leg
• Skin that feels warm

Symptoms of PE include:

• Trouble breathing
• Cough
• Chest pain
• Rapid heartbeat and breathing

Many people do not have any symptoms of PE.

Both DVT and PE require quick medical treatment. If you have DVT symptoms and are not in a health care setting, call your health care provider. If you have symptoms of PE, seek immediate medical attention.

What happens during a D-dimer test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You don't need any special preparations for a D-dimer test.

Are there any risks to a D-dimer test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

If your results show low or normal D-dimer levels in the blood, it means you probably don't have a clotting disorder.

But if you are being treated with blood thinner medicines, they may cause a false negative D-dimer test. This means your test results show that you don't have a clotting disorder, but you really do.

If your results show higher than normal levels of D-dimer, it may be a sign of a clotting disorder. Additional tests will be needed to show where the blood clot is located or what type of clotting disorder you have.

High D-dimer levels are not always caused by clotting disorders. A few other possible reasons why you may have high D-dimer levels include pregnancy, heart disease, rheumatoid arthritis, and recent surgery. Being older or immobilized (unable to move) may also cause a high D-dimer level.

If your D-dimer results were not normal, your provider will probably order more tests to make a diagnosis. To understand the results of a D-dimer test, your provider will consider your symptoms, medical history, and the results of other tests.

If you have questions about your results, talk to your provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a D-dimer test?

If your D-dimer test results were not normal, your provider may order one or more imaging tests to find out if you have a clotting disorder. These include:

• Doppler ultrasound, a test that uses sound waves to create images of your veins. This may help to find out if the blood in your veins is flowing as it should.
• 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. This may help to find blood clots or check if your blood vessels are damaged.
• Ventilation-perfusion (V/Q) scan. These are two tests that look for certain lung problems. These tests may be done separately or together. The ventilation scan measures how air moves in and out of your lungs. The perfusion scan measures how blood flows in the lungs. They both use small amounts of radioactive tracer to help a scanning machine check how well your lungs are working.