D-dimer optimal range and reference range
Compiled by Alina Radu, founder of Sera, from the published sources below · Last reviewed November 9, 2026
Sera's bands for D-dimer:
- Optimal 0 – 500 ng/mL FEU (0 – 500 μg/L FEU); out of range below 0 or above 500 ng/mL FEU.
Evidence grade: Established clinical threshold. A band edge that corresponds to a recognised diagnostic, risk or treatment threshold from a major clinical guideline or public-health body.
All units
| Unit | Optimal | Sufficient | Out of range |
|---|---|---|---|
| ng/mL FEU | 0 – 500 | — | below 0 or above 500 |
| μg/L FEU | 0 – 500 | — | below 0 or above 500 |
| mg/L FEU | 0 – 0.5 | — | below 0 or above 0.5 |
No separate Sufficient band is currently defined for this marker.
What the evidence says
Only ever a rule-out. Below 500 ng/mL FEU (0.5 mg/L FEU) is the standard cut-off for excluding venous thromboembolism in someone at low clinical probability. From age 50 laboratories and NICE allow an age-adjusted cut-off instead: age times 10 in ng/mL FEU, so 600 at 60 and 800 at 80. Sera does not apply that adjustment, so a result just above 500 in an older client may still be negative by their laboratory's rule. Infection, inflammation, surgery, pregnancy, malignancy and age all raise it, so a high value on its own means little, while a low value genuinely lowers the probability of thrombosis. Units are the real hazard: fibrinogen-equivalent units are twice D-dimer units for the same sample, so a DDU result entered against these bands reads as half of what it is. Cut-offs are also specific to the assay; the reporting laboratory's own cut-off takes precedence.
Assay: Results differ meaningfully between platforms and methods. Compare against the interval printed by the issuing laboratory before acting on a borderline value.
Sources
- D-Dimer (test 115188): age-adjusted cutoff — Labcorp test directory, 2026 · Laboratory / reference-interval sourceGives the age-adjusted cut-off for people over 50 as age divided by 100 in mg/L FEU, citing the American College of Physicians. This is the only evidenced threshold between 500 and 1000 ng/mL FEU, and it depends on age.
- Venous thromboembolic diseases: diagnosis, management and thrombophilia testing (NG158) — National Institute for Health and Care Excellence, 2023 · Clinical guidelineRecommendation 1.1.14: consider an age-adjusted D-dimer threshold for people aged over 50. Published March 2020, last updated August 2023. It gives no number, so it supports the note and not a band edge.
What D-dimer measures
A fragment released when cross-linked fibrin is broken down, indicating that clot has formed and is being dissolved somewhere in the body.
A rule-out test, not a rule-in one: it is raised by infection, inflammation, surgery, pregnancy, cancer and simple age, so a high result means very little on its own while a low one is genuinely reassuring. Units are the common trap — fibrinogen-equivalent units (FEU) are twice D-dimer units (DDU) for the same sample, so Sera labels the unit explicitly and a DDU result must not be entered against these.