Coagulation
D-dimer
D-dimer is a soluble fibrin degradation product released when plasmin breaks down cross-linked fibrin, so a raised level signals recent or ongoing clot formation and breakdown. At the point of care it is used mainly as a high-sensitivity rule-out aid for venous thromboembolism, always interpreted alongside a validated clinical pretest probability score.
Why it is measured
It helps to exclude deep vein thrombosis and pulmonary embolism in patients with low or intermediate pretest probability, where a result below the assay cutoff carries a high negative predictive value. A raised result is non-specific and prompts further imaging or testing rather than confirming a diagnosis on its own.
| Typical range | Indicative adult negative cutoff is below 0.5 mg/L FEU (500 ng/mL FEU), roughly equivalent to 0.25 mg/L DDU, but cutoffs, units and calibration vary by method and analyser. An age-adjusted threshold (age in years multiplied by 10, in micrograms/L FEU) is commonly applied above 50 years in low or intermediate risk patients. FEU and DDU results are not interchangeable, so the analyser's own stated cutoff must always be used. |
|---|---|
| Sample | Anticoagulated venous whole blood or plasma, with the required anticoagulant varying by device (for example heparin for the Roche CARDIAC D-Dimer, and citrate or EDTA for other point-of-care systems). Several cartridge systems also accept a small whole-blood volume (for example about 150 microlitres). Samples should be run promptly per the assay instructions, and grossly haemolysed or lipaemic specimens may affect optical immunoassay reads. |
| Turnaround | Approximately 8 to 21 minutes depending on the analyser: around 8 minutes on the cobas h 232 and up to roughly 21 minutes on the AQT90 FLEX. |
Point of care devices that report it
- Roche cobas h 232 (Roche CARDIAC D-Dimer test strip)
- Radiometer AQT90 FLEX (D-dimer immunoassay)
- QuidelOrtho Triage MeterPro (Triage D-Dimer Test)
- LumiraDx Platform (LumiraDx D-Dimer test)
Questions, answered
Does a normal point-of-care D-dimer rule out a clot on its own?
No. A result below the assay cutoff is only used to help exclude venous thromboembolism when combined with a validated clinical pretest probability score, such as the Wells score, in low or intermediate risk patients. It is not used in isolation and is not appropriate to rule out clots in high pretest probability patients, who proceed to imaging regardless.
Why do D-dimer results and cutoffs differ between analysers?
Different assays calibrate against different standards and report in different units, most commonly fibrinogen equivalent units (FEU) or D-dimer units (DDU), where roughly 1 DDU equals 2 FEU. Because methods are not standardised or directly interchangeable, results should be read against the cutoff stated for the specific device and not compared numerically across platforms.
What else can raise D-dimer apart from clots?
D-dimer is a sensitive but non-specific marker. Levels can rise with increasing age, pregnancy, recent surgery or trauma, infection and sepsis, inflammation, liver disease and malignancy. This is educational background only and any individual result should be interpreted by the responsible clinician in the full clinical context.