Interactive tool
Calculate the threshold and compare the value
Enter your age and D-dimer value. Check your laboratory's unit of measurement: the classic formula is calibrated on fibrinogen equivalent units (FEU); in laboratories that report in D-dimer units (DDU) the values are approximately half.
Come si usa
Instructions for use
Il principio
La regola è semplice: over 50 years the threshold becomes age × 10 µg/L FEU; up to 50 years the conventional threshold of 500 µg/L FEU remains. A 78-year-old patient therefore has a threshold of 780 µg/L: a value of 620 µg/L, which with the fixed threshold would have been "positive" and would have triggered a CT angiography, with the correct threshold is negative.
Condizione indispensabile
The D-dimer — at any threshold — serves to escludere thromboembolism in patients with low or intermediate pre-test probability (or “unlikely” in dichotomous models). In case of clinical probability alta the D-dimer does not even need to be requested: we proceed directly to imaging, because a negative result does not lower the post-test probability below the safety threshold.
Correct sequence
- Estimate the pre-test clinical probability with a validated tool: Wells per la TVP, Geneva or Wells for pulmonary embolism.
- Se la probabilità è alta → imaging diretto, niente D-dimero.
- If the probability is low or intermediate → High sensitivity D-dimer, compared to the age-corrected threshold.
- D-dimer below threshold → thromboembolism excluded, no imaging, no anticoagulation.
- D-dimer above threshold → pulmonary CT angiography (suspected for PE) or venous color Doppler ultrasound (suspected DVT).
Unit of measurement
- FEU (fibrinogen equivalent units): conventional threshold 500 µg/L, equivalent to 0.50 mg/L FEU or 500 ng/mL FEU. It is the unit on which the ADJUST-PE and YEARS studies were validated.
- DDU (D-dimer units): the values are about half; the conventional threshold corresponds to ~250 µg/L DDU and the formula becomes age × 5.
- If the laboratory report does not specify the unit, ask: this is the most common error and can lead to a patient with embolism being discharged.
Riferimenti clinici
Guidelines and interpretation
Evidenza a sostegno
The multicenter prospective study ADJUST-PE (Righini M. et al., JAMA 2014) enrolled 3346 patients with suspected pulmonary embolism: among those over seventy-five with probability clinically not high, the proportion of patients in whom embolism could be excluded without imaging is rose from 6.4% to 29.7% adopting the age-adjusted threshold. The 3-month thromboembolic event rate in untreated patients is remained below 0.5%, within the conventionally accepted safety margin.
Le ESC guidelines 2019 on the diagnosis and treatment of acute pulmonary embolism recommend the use of the age-corrected threshold as an alternative to the fixed threshold (class IIa, level B). THE'ASH 2018 (American Society of Hematology) and guidelines NICE NG158 ne riconoscono l'utilità nella popolazione anziana.
| Età | FEU threshold | Indicative DDU threshold |
|---|---|---|
| ≤ 50 years | 500 µg/L | 250 µg/L |
| 60 years old | 600 µg/L | 300 µg/L |
| 70 years old | 700 µg/L | 350 µg/L |
| 80 years old | 800 µg/L | 400 µg/L |
| 90 years old | 900 µg/L | 450 µg/L |
Conditions that raise D-dimer independently of thrombosis
A high D-dimer is not never diagnostic: It has high negative predictive value and low positive predictive value. It increases in pregnancy and the puerperium, active neoplasia, infection and sepsis, recent surgery, trauma, burns, disseminated intravascular coagulation, aortic dissection, renal and hepatic failure, heart failure, reabsorbing hematomas and in hospitalized patients in general. In these contexts the specificity collapses and the age correction it's not enough to recover it.
Alternative alla correzione per età
- Threshold adapted to clinical probability: l'algoritmo YEARS use 1000 ng/mL in patients without any of the three criteria and 500 ng/mL in the others; it is also validated during pregnancy (Artemis study).
- PEGeD (Kearon C. et al., NEJM 2019): threshold 1000 ng/mL with low Wells probability, 500 ng/mL with moderate probability.
- The two strategies should not be combined arbitrarily: adopt one and apply it consistently within the diagnostic path of your service.
During pregnancy, the D-dimer rises progressively with the gestational age and the correction for chronological age is meaningless. The algorithm validated in this population is YEARS adapted (Artemis study), which includes ultrasound compression of the lower limbs in patients with signs of DVT.
Bibliografia
Sources
- Righini M. et al., JAMA 2014 — Age-adjusted D-dimer cutoff levels to rule out pulmonary embolism: the ADJUST-PE study.
- ESC 2019 — Guidelines for the diagnosis and management of acute pulmonary embolism, European Heart Journal.
- Douma RA. et al., BMJ 2010 — Potential of an age adjusted D-dimer cut-off value to improve the exclusion of pulmonary embolism.
- NICE NG158 — Venous thromboembolic diseases: diagnosis, management and thrombophilia testing.
Quick consultation tool intended for healthcare personnel. It does not replace the original guidelines, the drug data sheets or the clinical judgment of the specialist. All calculations take place in the browser: no patient data is transmitted or stored on the server.