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.

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 obvious injury or don’t dissolve when they should. These conditions can be very serious and even life-threatening. A D-dimer test can show if you have one of these conditions.

Other names: fragment D-dimer, fibrin degradation fragment

What is it used for?

A D-dimer test is used to find out if 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.
• 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.
• 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.

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 include:

• Leg pain or tenderness
• Leg swelling
• Redness or red streaks on the legs

Symptoms of PE include:

• Trouble breathing
• Cough
• Chest pain
• Rapid heartbeat

This test is often done in an emergency room or other health care setting. If you have DVT symptoms and are not in a health care setting, call your health care provider. If you have symptoms of PE, call 911 or 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.

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.

If you have questions about your results, talk to your health care 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.
• 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.