D-dimer is a fragment left over after the body dissolves a clot. Its appearance in the blood means that clot formation and breakdown has been going on somewhere.
The main value of the test is in ruling out: a normal D-dimer when the probability is not high reliably excludes dangerous clots — deep vein thrombosis (DVT) and pulmonary embolism (PE). It is linked to the work of platelets and clotting.
Reference ranges
Approximate values (units depend on the lab):
| Normal | < 0.5 µg/mL (< 500 ng/mL FEU) |
| Age adjustment (> 50 years) | threshold ≈ age × 10 ng/mL |
| A rise | clots, but also many non-specific causes |
| Strength | a normal result rules out a clot |
What an elevated level means
A high D-dimer means active clot formation and breakdown, but does not by itself prove a specific clot.
Causes: deep vein thrombosis and pulmonary embolism, as well as pregnancy, inflammation and infection, recent surgery and trauma, cancer, older age, and DIC. So a high result calls for further investigation (vein ultrasound, CT) rather than an immediate diagnosis.
What a low level means
A normal (low) D-dimer is a valuable negative result: when the clinical probability is low or intermediate it reliably rules out deep vein thrombosis and pulmonary embolism, sparing unnecessary CT scans and treatment.
This is why the test is widely used in emergency departments as a "filter" when a clot is suspected.
How the test is done
D-dimer is measured in blood from a vein; no special preparation is needed. The test is ordered when a clot is suspected (a swollen, painful leg, sudden breathlessness).
The result is always interpreted together with the clinical probability: in people over 50 an age adjustment of the threshold is used to reduce the number of false-positive results.
What affects the value
- Clots (DVT, PE) — raise D-dimer.
- Pregnancy — raises it physiologically.
- Inflammation, infection, surgery, trauma — raise it.
- Cancer — raises it.
- Age — raises it (an age adjustment is needed).
- Anticoagulants — may lower the result.
Assess your cardiovascular risk
A tendency to clot is part of vascular risk; assess it:
Frequently asked questions
What does a high D-dimer mean?
That clot formation and breakdown is going on in the body. But the test is not very specific: a rise occurs in pregnancy, inflammation, infection, after surgery and in cancer. So a high result is a reason for further testing, not a ready diagnosis of a clot.
Why is D-dimer tested?
Mainly to rule out dangerous clots — deep vein thrombosis and pulmonary embolism. A normal result when the probability is not high reliably removes the suspicion and spares unnecessary investigations.
What is the age adjustment for D-dimer?
With age the D-dimer level naturally rises, which causes many false-positive results in older people. So after 50 the threshold is calculated as age × 10 ng/mL — this improves the accuracy of ruling out a clot.
Related terms
Sources
- MedlinePlus (NIH) — D-dimer Test
- D-dimer age-adjusted cutoff (review). NCBI
- D-dimer in cardiovascular disease (review). NCBI/PMC