Interactive tool
Apply the algorithm
Tick the criteria present and enter the D-dimer value. The algorithm automatically determines the applicable threshold and the result.
How to use it
Instructions
The three criteria
- Clinical signs of deep vein thrombosis — leg swelling, tenderness along the deep veins, asymmetry in circumference. This is the same “signs of DVT” criterion as in the Wells score.
- Haemoptysis.
- Pulmonary embolism is the most likely diagnosis — overall clinical judgement: of all the hypotheses that explain the clinical picture, PE is at the top of the list.
How the variable threshold works
| Criteria present | D-dimer threshold | If below threshold | If above threshold |
|---|---|---|---|
| None (0) | 1000 ng/mL FEU | PE ruled out | CT pulmonary angiography |
| One or more (≥ 1) | 500 ng/mL FEU | PE ruled out | CT pulmonary angiography |
Why this structure
The insight of the YEARS study is that D-dimer and clinical probability should not be treated as two separate steps, but as a single sliding threshold. A patient with none of the three criteria has such a low baseline probability that a doubled threshold is affordable; a patient with at least one criterion stays on the strict threshold. In practice this reduces CT angiography by about 14% compared with the Wells algorithm with a fixed threshold, with the same safety.
A single blood test
Unlike the classic algorithm, in YEARS D-dimer is always measured, at the same time as the clinical assessment: there is no branch in which the test is skipped. This simplifies the emergency department workflow, where the blood sample has often been sent before the doctor has finished estimating the probability.
The 500 and 1000 ng/mL thresholds are expressed in fibrinogen-equivalent units (FEU): 1000 ng/mL FEU = 1000 µg/L FEU = 1.0 mg/L FEU. In laboratories that report in D-dimer units (DDU) the corresponding values are about half.
Clinical references
Guidelines and interpretation
The YEARS study
Van der Hulle T. and colleagues (Lancet 2017) prospectively applied the algorithm to 3465 patients with suspected pulmonary embolism in 12 Dutch hospitals. The 3-month incidence of venous thromboembolism in patients in whom PE had been ruled out without imaging was 0.61% (95% CI 0.36–0.96), within the safety margin. CT angiography was avoided in 48% of patients, compared with 34% with the fixed-threshold Wells algorithm: 14 percentage points fewer scans.
YEARS in pregnancy: the Artemis study
Van der Pol LM. and colleagues (N Engl J Med 2019) adapted the algorithm to pregnancy, with one important change: in patients with clinical signs of deep vein thrombosis, compression ultrasound of the legs is performed first. If it shows a proximal DVT, the diagnosis is made and treatment starts without exposing the patient to radiation. Only if compression ultrasound is negative does the work-up continue with D-dimer according to the two-threshold rule.
In 498 pregnant women, the algorithm avoided CT angiography in 39% of cases (65% in the first trimester), with a 3-month event rate of 0.21%.
What the guidelines say
- ESC 2019: algorithms with a D-dimer threshold adapted to clinical probability, including YEARS, are an acceptable alternative to the fixed threshold and to age adjustment (class IIa, level B).
- ASH 2018: in pregnant patients with suspected pulmonary embolism, an algorithm that starts with venous ultrasound when leg symptoms are present is recommended to limit radiation exposure.
- NICE NG158: keeps the Wells + fixed-threshold D-dimer approach, but recognises adapted-threshold strategies as an option within local pathways.
YEARS, PEGeD and age adjustment are alternative strategies, each validated as a single package. Applying the 1000 ng/mL YEARS threshold and then also adjusting it for age, or mixing it with Wells stratification, produces an unvalidated pathway with an unknown rate of missed diagnoses. The department should adopt one algorithm and apply it consistently.
Limitations
- The third criterion (“PE is the most likely diagnosis”) is subjective and shows considerable inter-observer variability: it is the weak point of the algorithm, as it is in the Wells score.
- The algorithm is not validated in patients already on anticoagulants or in those with symptoms for more than 7 days.
- In hospitalised and frail elderly patients the specificity of D-dimer remains low even with a 1000 ng/mL threshold.
References
Sources
- van der Hulle T. et al., Lancet 2017 — Simplified diagnostic management of suspected pulmonary embolism (the YEARS study): a prospective, multicentre, cohort study.
- van der Pol LM. et al., N Engl J Med 2019 — Pregnancy-adapted YEARS algorithm for diagnosis of suspected pulmonary embolism (Artemis study).
- ESC 2019 — Guidelines for the diagnosis and management of acute pulmonary embolism.
- Kearon C. et al., N Engl J Med 2019 — Diagnosis of pulmonary embolism with d-dimer adjusted to clinical probability (PEGeD study).
Quick-reference tool for healthcare professionals. It does not replace the original guidelines, the summaries of product characteristics or the specialist's clinical judgement. All calculations run in the browser: no patient data is transmitted to or stored on any server.