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Blood Test Tracker

D-Dimer (FEU)

A blood test for fragments left when a clot breaks down, used to help rule out a blood clot and to follow clotting problems such as DIC.

AI-verified against cited sources. Awaiting expert reviewLOINC 48065-7

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What it is

When your body breaks down a blood clot, it releases small pieces called D-dimer. This test measures how much is in your blood. Many things besides a clot can raise it, including older age, pregnancy, recent surgery, infection and cancer. Because of that, the test is most useful when the result is low.

Why it matters

A D-dimer below the lab's cutoff, together with a low-risk assessment by a clinician, makes a clot in the leg or lung unlikely and can spare people imaging scans. A high result cannot show why it is high, so it is read together with symptoms and other findings. The test is also used with other clotting tests to follow disseminated intravascular coagulation (DIC).

If it’s high

A high D-dimer means more clot breakdown is happening than usual. This is common and often has harmless or temporary causes. It does not by itself mean you have a blood clot.

Common causes

  • Older age, since levels rise with age
  • Pregnancy, with levels climbing in each trimester
  • Recent surgery, injury or bleeding
  • Infection or other inflammation, including COVID-19
  • A hospital stay, or hard exercise before the blood draw
  • Other conditions such as atrial fibrillation, liver cirrhosis, kidney disease, diabetes, autoimmune disease or cancer
  • A blood clot in a leg vein (DVT) or in the lung (PE)
  • DIC (disseminated intravascular coagulation) in people who are seriously ill
  • Test interference from rheumatoid factor or other antibodies on some assays

What can help

  • Ask your clinician what is most likely behind a high result in your situation
  • If you have no symptoms of a clot and none of the conditions listed above, ask whether any follow-up is needed. A recent Italian consensus advises against routine scans, cancer screening or repeat testing for an unexplained high D-dimer in that situation
  • If you are pregnant, ask how your clinician interprets D-dimer, because standard cutoffs do not apply

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: up to 500 ng/mL FEU. Source: Mayo Clinic Laboratories (Extended Catalog), ARUP Laboratories, Quest Diagnostics Clinical Education Center, American Journal of Hematology, JAMA, Biochemia Medica, MedlinePlus (National Library of Medicine).

What can affect your result

  • Age: levels rise with age
  • Pregnancy: levels rise with each trimester
  • Recent surgery, injury, infection or a hospital stay
  • Hard exercise
  • The assay and its units (FEU or DDU), which change both results and cutoffs
  • Blood-thinning treatment, which can lower the result
  • Rheumatoid factor and similar antibodies, which can raise it on some assays
  • Rheumatoid factor and other antibodies in the blood can falsely raise results on some assays.
  • Blood-thinning treatment can lower D-dimer, and a clot that is older than about 7–10 days can leave D-dimer normal.
  • Different assays use different antibodies and calibrators, and report FEU or DDU units, so results and cutoffs cannot be compared between methods.

Reflects recent clot formation and breakdown. It can be normal when symptoms started more than about 7–10 days ago.

When to talk to a clinician

Get emergency care right away if you have signs of a blood clot, whatever a D-dimer result says: sudden shortness of breath, chest pain, coughing blood, a racing heartbeat, or a swollen, painful, warm leg or arm. A result above your lab's cutoff (500 ng/mL FEU at many labs, or age × 10 if you are 50 or older) means this test alone cannot rule out a clot, so talk with the clinician who ordered it soon.

Questions you could ask

  • Is an age-adjusted cutoff appropriate for me?
  • What do you think is most likely behind my high D-dimer?
  • Do my symptoms or risk factors mean I need more tests, or could this be from age, pregnancy, recent surgery or an illness?
  • Does my lab report FEU or DDU units, and what cutoff does it use?

Questions people ask

What is the difference between FEU and DDU?

They are two ways of reporting the same blood protein. FEU (fibrinogen equivalent units) numbers are roughly twice DDU (D-dimer units) numbers for the same sample, so a cutoff of 500 ng/mL FEU is about 250 ng/mL DDU. Check which one your report uses. This marker is for FEU results, and DDU results are tracked separately.

I am over 50. Why is my cutoff higher than 500?

D-dimer rises with age, so the usual cutoff of 500 gives many false alarms in older adults. For people 50 and older, many clinicians use an age-adjusted cutoff of age × 10 ng/mL FEU when checking whether a clot is likely. Your clinician decides which cutoff applies to you.

Does pregnancy raise D-dimer?

Yes. D-dimer normally rises through pregnancy, so a result above a standard cutoff can be typical. Cutoffs for pregnancy have not been firmly established, so clinicians read the result along with symptoms and other findings.

Show the science and sources

Units

  • 1 ng/mL FEU = 1 ng/mL FEU
  • 1 ng/mL FEU = 1 µg/L FEU
  • 1 ng/mL FEU = 0.001 µg/mL FEU
  • 1 ng/mL FEU = 0.001 mg/L FEU

Open the D-Dimer unit converter

Is a change real?

D-Dimer naturally varies about 25.2% from test to test in the same healthy person. Between two results from the same lab, a rise of 116% or more, or a fall of 54% or more, is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Systematic review and meta-analysis of within-subject and between-subject biological variation data of coagulation and fibrinolytic measurands (Hollestelle MJ et al.).

For clinicians and researchers

D-dimer is a degradation product of cross-linked fibrin, formed when plasmin digests fibrin stabilized by factor XIIIa, so it marks both coagulation activation and fibrinolysis. Assays are not standardized: they use different monoclonal antibodies and calibrators, there is no international standard, and results are expressed in fibrinogen equivalent units (FEU) or D-dimer units (DDU), with FEU roughly twice DDU. A reference value (about the 95th percentile of healthy people) is different from a clinical cutoff chosen for a sensitivity close to 100% for VTE, typically 500 or 250 µg/L depending on the method, and the reference value is the one used when evaluating DIC. A normal D-dimer with low pretest probability can exclude VTE; in ADJUST-PE, an age-adjusted cutoff (age × 10 µg/L at 50 and older) increased the share of patients in whom PE could be excluded without extra missed cases (3-month failure rate 0.3%, 1 of 331 patients between 500 µg/L and the adjusted cutoff). The SISET consensus lists causes of raised D-dimer, including surgery, hemorrhage, trauma, malignancy, sepsis, age, pregnancy, DIC, atrial fibrillation, hospitalization, exercise, inflammation, aortic dissection, cirrhosis, diabetes and renal disease, and notes that cutoffs for pregnancy are not established. False negatives can occur with antithrombotic therapy, hypofibrinolysis or symptoms older than 7–10 days.

LOINC 48065-7 (primary), 48067-3, 111766-2. Specimen: plasma.

Sources

  1. D-Dimer, Plasma (test DDITT), Mayo Clinic Laboratories (Extended Catalog)
  2. D-Dimer (ARUP test 0030057), ARUP Laboratories
  3. Facts and Misfacts on D-Dimer Testing. Consensus Guidance From the Italian Society on Thrombosis and Hemostasis (SISET), American Journal of Hematology (2025)
  4. Age-adjusted D-dimer cutoff levels to rule out pulmonary embolism: the ADJUST-PE study, JAMA (2014)
  5. Croatian Society of Medical Biochemistry and Laboratory Medicine: National recommendations for blood collection, processing, performance and reporting of results for coagulation screening assays prothrombin time, activated partial thromboplastin time, thrombin time, fibrinogen and D-dimer, Biochemia Medica (2019)
  6. D-dimer Test, MedlinePlus (National Library of Medicine)
  7. D-dimer test frequently asked questions (Quest test code 8659), Quest Diagnostics Clinical Education Center

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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