D-dimer
Protein fragments produced when blood clots dissolve
Also known as
Definition
D-dimers are small protein fragments produced when the body dissolves a blood clot. They are normally barely present in the blood unless the body is forming or breaking down clots. The test helps assess whether further tests for a clotting disorder such as deep vein thrombosis or pulmonary embolism are needed. It is also used to monitor disseminated intravascular coagulation (DIC) during treatment.
| Parameter | Value |
|---|---|
| Unit | Varies by test method (as stated in the report) |
| Reference Range | A normal result is negative, meaning below the cut-off of the respective lab. Cut-off and unit depend on the test method; the information in your own report is what counts. Discuss the result with your doctor. |
Agree on your personal target range with your doctor.
↓ What a low value means
A low or negative value makes a clotting disorder less likely; this is the strength of the test. You should still have any symptoms checked by a doctor. Blood-thinning medicines can, however, cause a false negative result. In treated DIC, a normal or falling value may indicate that treatment is working.
↑ What a high value means
An elevated or positive value may indicate that the body is forming and breaking down blood clots. The test does not show where a clot is or why it formed; further tests such as ultrasound or other imaging are needed for that. Elevated values also occur without a clot, for example in pregnancy, after surgery or injury, with heart or liver disease, rheumatoid arthritis, high blood lipid or triglyceride levels, in older age or when immobilized. Interpretation is up to your doctor.
When to test
No special preparation is needed. The test is ordered when a blood clot is suspected, for example with pain, swelling, warmth or discoloration of a leg, and to monitor DIC. Sudden shortness of breath, chest pain or coughing up blood are an emergency: seek medical help immediately.
Frequently asked questions
Why is a negative D-dimer test more informative than a positive one? +
D-dimers can rise for many reasons, even without a clot, for example in pregnancy or after surgery. A negative result, by contrast, makes a clotting disorder less likely. The test is therefore most useful when it is negative or when other causes can be ruled out.
Does the test show where a clot is? +
No. An elevated value is usually followed by imaging tests, for example a Doppler ultrasound of the veins, CT angiography or a ventilation-perfusion scan of the lungs.
Can medicines affect the result? +
Yes. Blood-thinning medicines can lead to a false negative result. So tell your doctor which medicines you take.
Does age play a role? +
Yes. MedlinePlus lists older age as a possible reason for elevated values without a clot; the encyclopedia explicitly mentions being over 80 years old. The result is therefore always assessed together with symptoms, medical history and other findings.
D-dimer
Sources
Last updated: October 05, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.