D-Dimer
D-Dimer
What this test measures
D-dimer is a protein fragment produced when a blood clot dissolves. It's mainly used to help rule out blood clots like deep vein thrombosis (DVT) or pulmonary embolism (PE).
Understanding the numbers
Typical range: Less than 500 µg/L (may vary by lab)
A normal D-dimer makes a blood clot very unlikely. However, many things can raise D-dimer, so a high result doesn't always mean you have a clot.
- Normal: 0–500 µg/L
- Mildly raised: 500–1000 µg/L
- Moderately raised: 1000–3000 µg/L
- Markedly raised: 3000–5000 µg/L
Key numbers
- 500 µg/L — Standard upper limit
- 1000 µg/L — Above = imaging usually needed when clot suspected
- 1000 µg/L — Age-adjusted: age × 10 µg/L in patients over 50
NICE NG158: in patients with low clinical probability (Wells score) of DVT or PE, a normal D-dimer safely rules out the clot. A raised D-dimer is non-specific — it rises in pregnancy, infection, inflammation, cancer and older age. Age-adjusted D-dimer (age × 10 µg/L for patients over 50) improves specificity.
Ranges can vary slightly between laboratories — your report may show slightly different numbers. This page does not read or interpret your result; your GP looks at it alongside your history and other tests.
What a higher-than-normal result can mean
- May indicate a blood clot, but further tests are usually needed
- Can be raised by infection, inflammation, or recent surgery
- Pregnancy, cancer, and liver disease can raise D-dimer
- D-dimer naturally increases with age
Questions you could ask your GP
- Does my result rule out a blood clot?
- Do I need any further tests like an ultrasound or CT scan?
- What might be causing my raised D-dimer?
- Am I at risk of blood clots in the future?
Example stories
These are made-up examples to show how results are talked about in real appointments. They are not real patients.
Low-probability PE — normal D-dimer
Callum had pleuritic chest pain after a short flight. Wells score was low. D-dimer was 280.
What the GP said: “With your low risk score and normal D-dimer, a pulmonary embolism is effectively ruled out. Your symptoms are probably musculoskeletal — come back if the pain persists or you become breathless.”
What happened next: Symptoms resolved without treatment or imaging.
Used correctly — in low-risk patients — a normal D-dimer safely rules out DVT and PE. That saves radiation, contrast exposure and anxiety.
High D-dimer — DVT confirmed
Gloria had a swollen painful left calf after a long coach journey. D-dimer 3200. Ultrasound showed a popliteal DVT.
What the GP said: “The D-dimer and ultrasound confirm DVT. I'll start you on apixaban — a tablet blood thinner — for three to six months. Watch for symptoms of PE (breathlessness, chest pain) and come back immediately if they happen.”
What happened next: Apixaban was continued for six months; her leg recovered without long-term swelling.
D-dimer is a trigger for imaging in higher-risk patients, not a stand-alone diagnostic test. A high D-dimer with the right symptoms supports imaging — and imaging confirms.
Age-adjusted D-dimer
Parveen had calf pain; D-dimer was 680. Standard cut-off is 500 — but age-adjusted cut-off is 720.
What the GP said: “Using the age-adjusted D-dimer (10 × your age), your result is actually within range. Combined with your low clinical probability, we can safely avoid a scan.”
What happened next: Parveen's pain settled over a week; no DVT.
In patients over 50, using age × 10 µg/L as the cut-off reduces unnecessary imaging without missing clinically significant clots — endorsed by NICE and reduces anxiety.
High D-dimer from non-clot causes
Esther had breathlessness. D-dimer 1800. CT pulmonary angiogram was negative; she had pneumonia instead.
What the GP said: “Your D-dimer was raised because of the pneumonia and the inflammation, not a clot. The scan ruled out a PE — we treat the pneumonia instead.”
What happened next: Amoxicillin treated the pneumonia; D-dimer was normal two weeks later.
A raised D-dimer does not equal a clot. Infection, inflammation, surgery, cancer, pregnancy and older age all raise it. The test is most useful for ruling out — not ruling in.
Before you act on anything here
This page is general information, written to help you understand — it is not personal medical advice and it cannot tell you what is right for you. Talk to your own GP, pharmacist or nurse about your own health.
- Need help now but it's not an emergency? Call NHS 111 or use 111.nhs.uk.
- Emergency? Call 999 or go to A&E.