D-dimer Test

A D-dimer test is a blood test usually used to help check for or monitor blood clotting problems. A positive test means the D-dimer level in your body is higher than normal and suggests you might have blood clots.

What is being tested?

This test measures the amount of D-dimer, which is normally undetectable, in your blood. Blood clots form whenever a blood vessel is damaged, whether that’s by an injury or by atherosclerosis, or when blood flow is restricted, such as by a vessel being compressed for a long time. When you have an injury, your body creates a blot clot to stop blood from leaking out of your blood vessels. D-dimer is a type of protein your body produces to break down the blood clot.

Why would I need this test?

Your doctor might ask you to have this test if he or she suspects you have blood clotting problems or wants to rule them out. These blood clotting problems include:

  • deep vein thrombosis (DVT) — clot formation in the veins, usually in the legs
  • pulmonary embolism — a blockage in an artery in the lung
  • disseminated intravascular coagulation — a condition that prevents your blood clotting normally
  • blood coagulation caused by venom of certain species of snake, such as brown snake. Learn more about symptoms caused by snake bites

If you are undergoing treatment for disseminated intravascular coagulation, your doctor may use the D-dimer test to monitor your condition.

How to prepare for this test

No preparation is needed for this test. A blood sample is taken from a vein in your arm.

Understanding your results

A higher than normal D-dimer level might mean you have had a significant blood clot. However, the test does not tell where the clot was or what caused it.

Other health problems can also cause the D-dimer level to go up. Therefore, the D-dimer test is not the only test used to diagnose a disease or condition. It is usually used with other blood tests and imaging scans.

If the D-dimer test is positive, then you might be sent for imaging. A normal D-dimer level usually indicates a clotting problem is unlikely.

More information

Visit Lab Tests Online website for more information about D-dimer testing. You can also read more about blood tests in general.

Read our Guide to blood testing to learn more about blood tests in general with information such as:

  • what to consider before having the test
  • what happens during a blood test
  • results accuracy
  • blood tests cost


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