A D-dimer test is a blood test that checks for, or monitors, blood-clotting problems. A positive test means the D-dimer level in the body is higher than normal and suggests someone might have blood clots.
The AstraZeneca COVID-19 vaccine has been linked to a very rare blood-clotting disorder called 'thrombosis with thrombocytopenia syndrome’ (TTS). You can read about it here. If you're experiencing any symptoms following a COVID-19 vaccination, you can use the COVID-19 Vaccine Side Effect Checker.
What is a D-dimer test?
This test measures the amount of D-dimer, a type of protein the body produces to break down a blood clot.
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. D-dimer is normally undetectable in the blood but it is produced when the body is trying to break down a blood clot.
Why would I need this test?
Your doctor might ask you to have this test if they suspect 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 the 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 do I prepare for a D-dimer test?
No preparation is needed for this test. A blood sample is taken from a vein in the 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.
Where to get 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 this guide to blood testing to learn more about blood tests, including:
- what to consider before having the test
- what happens during a blood test
- results accuracy
- blood test costs
Learn more here about the development and quality assurance of healthdirect content.
Last reviewed: August 2020