Pulmonary embolism (PE) represents a critical diagnostic challenge in emergency medicine and internal medicine. The condition requires prompt recognition and treatment, yet overdiagnosis can lead to unnecessary radiation exposure, contrast-induced nephropathy, and increased healthcare costs. The YEARS algorithm emerged as a refined clinical decision tool designed to optimize the diagnostic pathway for suspected PE by combining clinical assessment with D-dimer testing in a more efficient manner than previous approaches.

Background and Development

The YEARS algorithm was developed to address limitations in existing diagnostic strategies for pulmonary embolism. Traditional approaches, such as the Wells score combined with D-dimer testing, often resulted in a high number of false-positive D-dimer results, leading to unnecessary computed tomography pulmonary angiography (CTPA) studies. The YEARS study, a large prospective cohort study, sought to validate a simplified approach that could reduce imaging while maintaining diagnostic safety.

The algorithm derives its name from the three clinical criteria it evaluates, though the acronym itself doesn't spell out "YEARS" but rather represents a streamlined assessment tool. The development team recognized that by adjusting D-dimer thresholds based on the presence of specific clinical criteria, they could improve the specificity of the diagnostic pathway without compromising sensitivity.

Clinical Criteria: The Three YEARS Items

The YEARS algorithm evaluates three specific clinical criteria, each representing important clinical indicators of potential pulmonary embolism:

1. Clinical Signs of Deep Vein Thrombosis (DVT)

This criterion focuses on physical examination findings that suggest the presence of deep vein thrombosis, which is often associated with pulmonary embolism. Clinical signs include:

• Unilateral leg swelling, particularly if asymmetric
• Pain or tenderness along the deep venous system
• Warmth or erythema over the affected area
• Palpable cord along a superficial or deep vein
• Positive Homan's sign (though less reliable)

The presence of clinical signs of DVT increases the likelihood that a patient presenting with respiratory symptoms may have a pulmonary embolism, as DVT and PE often represent different manifestations of venous thromboembolism (VTE).

2. Hemoptysis

Hemoptysis, or coughing up blood, is a classic symptom of pulmonary embolism, though it occurs in a minority of cases. When present, hemoptysis suggests that the embolus may have caused pulmonary infarction or significant pulmonary vascular compromise. The presence of hemoptysis in a patient with suspected PE increases the clinical suspicion and is therefore included as one of the YEARS criteria.

It is important to distinguish true hemoptysis from other sources of bleeding, such as epistaxis, gastrointestinal bleeding, or bleeding from the oropharynx. True hemoptysis typically presents as bright red or blood-streaked sputum and is associated with coughing.

3. PE as the Most Likely Diagnosis

This criterion requires clinical judgment and represents the clinician's assessment that pulmonary embolism is the most likely diagnosis based on the overall clinical presentation. This evaluation considers:

• Patient history, including risk factors for VTE
• Presenting symptoms (dyspnea, chest pain, syncope)
• Physical examination findings (tachypnea, tachycardia, signs of right heart strain)
• Initial investigations (chest X-ray, electrocardiogram, arterial blood gas)
• Exclusion of alternative diagnoses that could explain the presentation

This criterion acknowledges that clinical gestalt, when properly applied, has significant diagnostic value. It requires the clinician to synthesize multiple pieces of information and determine whether PE is more likely than alternative diagnoses such as pneumonia, heart failure, or anxiety.

D-dimer Thresholds: The Adaptive Approach

The innovative aspect of the YEARS algorithm lies in its use of adaptive D-dimer thresholds based on the number of clinical criteria present. This approach recognizes that patients with more clinical indicators of PE require a lower threshold for further investigation, while those with fewer indicators can safely use a higher threshold.

Threshold Determination

The algorithm uses two distinct D-dimer thresholds:

• 0 YEARS items present: D-dimer threshold of 1000 ng/mL (or 1.0 mg/L fibrinogen equivalent units)
• 1 or more YEARS items present: D-dimer threshold of 500 ng/mL (or 0.5 mg/L fibrinogen equivalent units)

This adaptive threshold system improves the specificity of D-dimer testing. When no clinical criteria are present, the higher threshold (1000 ng/mL) reduces false-positive results, as patients with low clinical suspicion are less likely to have PE even with modestly elevated D-dimer levels. Conversely, when clinical criteria are present, the lower threshold (500 ng/mL) ensures that patients with higher clinical suspicion are appropriately evaluated, even with lower D-dimer elevations.

Algorithm Workflow

The YEARS algorithm follows a systematic, step-by-step approach:

Step 1: Clinical Assessment

The first step involves a thorough clinical evaluation to determine which, if any, of the three YEARS criteria are present. This requires:

• Complete history taking, focusing on risk factors and symptoms
• Comprehensive physical examination, including assessment for DVT signs
• Review of initial diagnostic tests (chest X-ray, ECG, basic laboratory studies)
• Clinical judgment regarding the likelihood of PE versus alternative diagnoses

Step 2: D-dimer Testing

Once the clinical criteria have been assessed, a D-dimer test is ordered. D-dimer is a fibrin degradation product that becomes elevated in the presence of active thrombosis. The test should be performed using a validated assay, and results should be reported in ng/mL or converted to the appropriate units for comparison with the threshold.

It is crucial to note that D-dimer levels can be elevated in numerous conditions beyond VTE, including:

• Pregnancy
• Malignancy
• Infection or inflammation
• Recent surgery or trauma
• Advanced age
• Renal failure
• Liver disease

Therefore, D-dimer should always be interpreted in the context of clinical presentation and the YEARS criteria.

Step 3: Threshold Application and Interpretation

After obtaining the D-dimer result, the appropriate threshold is applied based on the number of YEARS items present:

If D-dimer is below the threshold:

• PE can be ruled out with high confidence
• No imaging studies (CTPA or V/Q scan) are required
• Alternative diagnoses should be considered
• Clinical follow-up should be arranged as appropriate

If D-dimer is at or above the threshold:

• PE cannot be ruled out
• Further imaging is required (typically CTPA)
• Consider empiric anticoagulation while awaiting imaging, especially in high-risk patients
• Urgent clinical assessment and monitoring

Clinical Validation and Performance

The YEARS algorithm has been extensively validated in multiple studies, demonstrating both safety and efficacy in clinical practice.

Key Validation Studies

The original YEARS study, a large prospective cohort study, demonstrated that the algorithm could safely exclude PE in a significant proportion of patients without requiring imaging. Subsequent validation studies and meta-analyses have confirmed these findings across diverse patient populations.

Performance Metrics

Systematic reviews and meta-analyses encompassing approximately 14,000 patients have demonstrated:

• Sensitivity: Approximately 96% for excluding PE, meaning the algorithm correctly identifies 96% of patients who do not have PE
• Specificity: Approximately 50%, indicating that about half of patients with elevated D-dimer levels will not have PE
• Negative Predictive Value: Very high, meaning that when the algorithm rules out PE, it is correct in the vast majority of cases
• Positive Predictive Value: Moderate, reflecting the fact that many conditions other than PE can cause D-dimer elevation

Clinical Outcomes

Beyond diagnostic accuracy, the YEARS algorithm has demonstrated important clinical benefits:

• Reduced Imaging: Significant reduction in the number of CTPA studies performed, decreasing radiation exposure and contrast use
• Faster Decision-Making: Studies have shown approximately 60 minutes shorter emergency department visit times compared to conventional diagnostic approaches
• Earlier Treatment: For patients with confirmed PE, treatment initiation was expedited by approximately 53 minutes
• Cost-Effectiveness: Reduced imaging leads to lower healthcare costs while maintaining patient safety

Advantages of the YEARS Algorithm

The YEARS algorithm offers several advantages over traditional diagnostic approaches:

Simplicity

Unlike scoring systems that require complex calculations or multiple weighted factors, the YEARS algorithm uses a simple binary assessment of three clinical criteria. This simplicity enhances usability and reduces the likelihood of calculation errors.

Adaptive Thresholds

The use of adaptive D-dimer thresholds based on clinical criteria represents a more nuanced approach than fixed thresholds. This allows the algorithm to be more specific in low-risk patients while maintaining sensitivity in higher-risk patients.

Reduced Imaging

By using higher D-dimer thresholds in patients without clinical criteria, the algorithm reduces unnecessary imaging studies. This is particularly important given concerns about radiation exposure, contrast-induced nephropathy, and healthcare costs.

Clinical Integration

The algorithm integrates seamlessly into clinical workflow, as it relies on standard history, physical examination, and laboratory testing that are already part of the evaluation of patients with suspected PE.

Validation

Extensive validation in large, prospective studies provides confidence in the algorithm's safety and effectiveness across diverse patient populations.

Limitations and Considerations

While the YEARS algorithm is a valuable clinical tool, several limitations and considerations must be acknowledged:

D-dimer Limitations

D-dimer testing has inherent limitations that apply to the YEARS algorithm:

• Elevated in many non-thrombotic conditions, limiting specificity
• Less reliable in certain populations (elderly, pregnant women, hospitalized patients)
• Requires appropriate units (ng/mL) for threshold comparison
• Different D-dimer assays may have varying performance characteristics

Clinical Judgment Requirement

The criterion "PE as the most likely diagnosis" requires clinical judgment, which introduces some subjectivity. Different clinicians may assess the same patient differently, potentially affecting the algorithm's application. However, this also allows for incorporation of clinical experience and patient-specific factors.

Population Considerations

While validated in diverse populations, the algorithm may perform differently in specific subgroups:

• Pregnant patients (D-dimer naturally elevated)
• Patients with malignancy (D-dimer often elevated)
• Hospitalized patients (higher baseline D-dimer)
• Elderly patients (age-related D-dimer elevation)

Alternative Diagnoses

The algorithm focuses specifically on PE and does not address the evaluation of alternative diagnoses. Clinicians must remain vigilant for other conditions that could explain the patient's presentation, such as pneumonia, heart failure, or anxiety.

Not a Replacement for Clinical Judgment

The YEARS algorithm is a decision support tool, not a replacement for clinical judgment. In certain situations, such as high clinical suspicion despite negative algorithm results, or in patients with contraindications to testing, clinical judgment should prevail.

Comparison with Other Diagnostic Tools

The YEARS algorithm should be understood in the context of other available diagnostic tools for PE:

Wells Score

The Wells score is a more complex scoring system that assigns points to various clinical features. While it has been widely validated, it requires calculation and may be less user-friendly than the YEARS algorithm. The YEARS algorithm offers similar or better performance with greater simplicity.

PERC Rule

The Pulmonary Embolism Rule-out Criteria (PERC) rule is used to identify patients in whom PE can be ruled out without D-dimer testing. The YEARS algorithm and PERC rule can be complementary, with PERC potentially identifying very low-risk patients who don't need any testing.

Fixed D-dimer Thresholds

Traditional approaches using fixed D-dimer thresholds (typically 500 ng/mL) result in more false-positive results and unnecessary imaging. The adaptive thresholds in the YEARS algorithm address this limitation.

Implementation in Clinical Practice

Successful implementation of the YEARS algorithm requires attention to several factors:

Education and Training

Healthcare providers must be educated about the algorithm, its criteria, and its interpretation. This includes understanding the three YEARS items, the adaptive threshold system, and the appropriate next steps based on results.

D-dimer Assay Selection

Clinicians must be aware of the D-dimer assay used in their institution and ensure that results are reported in units compatible with the algorithm thresholds (ng/mL). Some assays report results in different units, requiring conversion.

Clinical Documentation

Documentation should clearly indicate which YEARS criteria were assessed, the D-dimer result, the threshold applied, and the clinical decision made. This facilitates quality improvement and ensures appropriate follow-up.

Quality Improvement

Institutions implementing the YEARS algorithm should monitor outcomes, including rates of imaging, missed diagnoses, and patient outcomes. This allows for continuous improvement and identification of areas where the algorithm may need adjustment.

Integration with Clinical Pathways

The algorithm should be integrated into broader clinical pathways for the evaluation of suspected PE, including consideration of alternative diagnoses, appropriate use of imaging, and anticoagulation protocols.

Special Populations

Certain patient populations require special consideration when applying the YEARS algorithm:

Pregnant Patients

D-dimer levels naturally increase during pregnancy, potentially affecting the algorithm's performance. However, the YEARS algorithm has been studied in pregnant patients and may still be useful, though clinical judgment remains paramount. The higher threshold (1000 ng/mL) when no YEARS items are present may be particularly helpful in this population.

Patients with Malignancy

Malignancy is associated with elevated D-dimer levels, which can complicate interpretation. However, patients with malignancy also have increased risk of VTE, making accurate diagnosis important. The YEARS algorithm can still be applied, but clinicians should be aware of the higher likelihood of false-positive D-dimer results.

Elderly Patients

Advanced age is associated with elevated D-dimer levels, potentially affecting the algorithm's specificity. However, age is also a risk factor for PE, making accurate diagnosis crucial. The adaptive threshold system helps address this challenge.

Hospitalized Patients

Hospitalized patients often have elevated D-dimer levels due to various factors, including immobility, surgery, and underlying medical conditions. The YEARS algorithm may be less specific in this population, but it can still provide valuable guidance when applied thoughtfully.

Future Directions

Research continues to refine and improve the diagnostic approach to pulmonary embolism. Future directions may include:

• Further validation in specific patient populations
• Integration with other biomarkers or clinical tools
• Development of age-adjusted or population-specific thresholds
• Use of machine learning or artificial intelligence to enhance diagnostic accuracy
• Long-term outcome studies to assess the algorithm's impact on patient care

As our understanding of pulmonary embolism and diagnostic tools evolves, the YEARS algorithm will likely continue to be refined and integrated with other approaches to optimize patient care.