A D-dimer test measures how much D-dimer protein is in the blood. This protein is present when blood clots break down. A positive result of 0.50 milligrams per liter (mg/L) or higher may indicate blood clots somewhere in the body.

D-dimer is a protein the body releases when blood clots break down. Its presence in the blood or urine may indicate that a person has developed a clot.

This article explains the D-dimer test and what the results mean. It also outlines the next steps following a positive D-dimer test.

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A D-dimer test is a blood test to determine the levels of D-dimer protein in the body.

The test can help detect deep vein thrombosis (DVT), pulmonary embolism (PE), and other blood clots. DVT occurs when a person develops blood clots in a deep vein, such as in the leg. A PE is a blockage in the pulmonary artery.

Any healthcare professional trained in blood tests can carry out a D-dimer test. After taking a blood sample, they send it to a laboratory for analysis.

Learn more about the D-dimer test here.

According to a 2022 article, a typical D-dimer level is less than 0.50 mg/L of fibrinogen equivalent units (FEU). A positive D-dimer is 0.50 mg/L or higher, indicating that a person may have blood clots.

A positive D-dimer test may suggest a clotting disorder. However, it cannot show the type of clotting disorder or the location of blood clots.

D-dimer results typically provide the following information:

  • the name of the test
  • the exact measurement of D-dimer in the blood
  • the typical range and whether the test result lies within it

A positive test result is not within the typical range and may indicate the presence of blood clots. A negative result, within the typical range, suggests an absence of blood clots.

Depending on the results of a D-dimer test, doctors may recommend further testing.

A high or positive D-dimer test suggests there may be blood clots somewhere in the body.

However, several other things can cause an elevated test result, including:

A high D-dimer test result can also occur in certain people without a blood clot, such as the following:

In these situations, doctors may recommend further tests to help with diagnosis.

False negatives and false positives can occur in D-dimer tests.

A false negative is when a D-dimer test does not show a positive result even though the person has blood clots.

In the case of a false positive, a D-dimer test shows a positive result even though the person does not have a condition causing blood clots.

Because of this, doctors will not use D-dimer tests as the only diagnostic tool but rather as an indicator to guide their next steps.

Doctors may recommend the following tests after a positive D-dimer result:

  • a coagulation profile, a series of blood tests that tell doctors how a person’s blood clots
  • an upper leg vein ultrasound
  • a Doppler ultrasound
  • a CT angiography, which is a type of X-ray to check blood vessels
  • a ventilation-perfusion scan, which uses X-ray scans to track air and blood flow in the lungs

These tests can confirm the D-dimer test result and allow doctors to determine where clots are in the body if present. Treatment can then quickly begin.

A doctor may recommend a D-dimer test if someone has symptoms of a blood clotting disorder. People often have the test in an emergency room or healthcare setting.

The test may help doctors diagnose the following conditions:

DVT

DVT is a blood clot in a deep vein that can break off and travel through the bloodstream to the lungs, causing a PE. These clots typically develop in the lower leg, pelvis, or thigh. However, they can also occur in the arm.

Symptoms of DVT include:

PE

A PE is a blood clot in the lungs. PEs can develop when a blood clot from another area of the body travels to the lungs and blocks an artery. PE is a serious medical condition that can be life threatening without immediate treatment.

Symptoms of a PE include:

Disseminated intravascular coagulation

According to the National Heart, Lung, and Blood Institute (NHLBI), disseminated intravascular coagulation (DIC) occurs when the body’s clotting system starts to malfunction, and small clots form throughout the body. This damages blood vessels, causing them to leak and leading to uncontrolled bleeding.

The NHLBI states that DIC can be life threatening without prompt diagnosis and treatment.

Stroke

A stroke is a sudden and severe episode of neurological damage to the brain. It can cause disability or even be fatal. Strokes occur when a blockage in one or more blood vessels in an area of the brain prevents blood from reaching that area.

Learn how to recognize the symptoms of a blood clot here.

Blood clotting is a process that occurs in the body to stop bleeding. It is the body’s natural way of repairing damage to the blood vessels.

The NHLBI explains that the process starts when an injury causes a break in the wall of a blood vessel and blood escapes. This triggers cells around the break to release chemicals, which tell the spleen to release platelets.

At the injury site, platelets stick together and attach to the vessel wall, forming a clot. The clot helps seal off the break so the immune system can repair the damage without further bleeding.

The blood clot then begins to dissolve, releasing D-dimer protein as part of the process.

If someone has a clotting condition, their body has trouble forming clots or making them quickly enough after an injury or surgery. They may experience heavy bleeding or pain from an open wound for days or weeks.

Learn more about conditions affecting coagulation here.

A positive D-dimer result can tell doctors whether a person may have blood clots somewhere in the body. The test is a vital step toward diagnosis and treatment.

Further tests can help doctors locate blood clots and understand their causes. Treatment often includes anticoagulation medication and wearing compression stockings to prevent further clots.

A 2022 article refers to the following statistics regarding the outlook for people with DVT and PE:

  • Many cases of DVT resolve without treatment, although the risk of recurrence is 25%.
  • Approximately 6% of people with DVT and 12% with PE die within 1 month of receiving a diagnosis.
  • 43% of people with DVT develop a condition called post-thrombotic syndrome within 2 years.

Although most cases of DVT resolve without mechanical removal, they still require treatment.

The D-dimer test can show the presence of D-dimer protein, which the body makes while breaking down blood clots. Doctors often order the test in an emergency room or healthcare setting if a person has symptoms of deep vein thrombosis or a pulmonary embolism.

A reading lower than 0.50 mg/L FEU is within the typical range. A reading of 0.50 or higher is a positive result and suggests the presence of clots.

However, the D-dimer test is less specific than other tests. While it is a useful diagnostic tool, doctors usually request additional tests to confirm a diagnosis.

Doctors also use the test to help rule out clotting as the cause of certain symptoms.