For patients over 50 with suspected pulmonary embolism and a non-high clinical probability, the age-adjusted threshold is the patient's age multiplied by 10, in µg/L fibrinogen-equivalent units: 750 for a 75-year-old, instead of the fixed 500. Check which units your laboratory reports, because D-dimer-unit assays need halving of these values.
The adjustment only applies after clinical probability has been assessed with a validated score. A patient with high clinical probability goes straight to imaging, whatever the D-dimer.
- Assess clinical probability first with Wells, revised Geneva or YEARS.
- In patients over 50, use age × 10 µg/L (FEU) as the D-dimer cut-off.
- Confirm whether your laboratory reports FEU or D-dimer units before applying the rule.
- Do not use a D-dimer to rule out PE when clinical probability is high; image instead.
Why it matters
The fixed cut-off loses specificity with age, sending many older patients for unnecessary scans.
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