What is the PIOPED (Prospective Investigation of Pulmonary Embolism Diagnosis) study?

The PIOPED Study: A Landmark Investigation in Pulmonary Embolism Diagnosis

The PIOPED (Prospective Investigation of Pulmonary Embolism Diagnosis) study was a groundbreaking multi-institution investigation designed to evaluate various conventional methods for diagnosing pulmonary embolism, particularly focusing on the accuracy of ventilation-perfusion (V/Q) lung scanning compared to pulmonary angiography. 1

Key Features and Findings

Study Design and Purpose

• Conducted as a prospective multi-center investigation
• Primary aim was to assess the diagnostic accuracy of V/Q scanning for pulmonary embolism (PE)
• Used pulmonary angiography as the gold standard reference test

Major Contributions to Clinical Practice

1. Clinical Probability Assessment

   • First major study to report and validate gestalt clinical assessment for PE 1
   • Demonstrated that clinician assessment of PE likelihood (0-100%) correlated with actual PE prevalence
   • Categorized patients into risk groups:
     • Low risk (0-19% probability): 9.2% had PE
     • Intermediate risk (20-79% probability): 29.9% had PE
     • High risk (80-100% probability): 67.8% had PE

2. V/Q Scan Interpretation

   • Established a standardized classification system for V/Q scan results 1
   • Demonstrated good interobserver agreement for classifying scans as normal or high probability, but lower agreement for intermediate or low probability categories 2
   • Found that PE was present in:
     • 87% of patients with high probability scans
     • 30% of patients with intermediate probability scans
     • 14% of patients with low probability scans
     • <1% of patients with normal scans 2

3. Integration of Clinical Assessment with Imaging

   • Demonstrated that combining clinical probability with V/Q scan results improved diagnostic accuracy 1
   • When clinical assessment and V/Q results were concordant:
     • High probability scan + high clinical suspicion: ~90% had PE
     • Low probability scan + low clinical suspicion: only 4% had PE 2
   • However, 64% of patients fell into indeterminate categories requiring further testing 1

Clinical Impact and Legacy

Diagnostic Algorithm Development

• Led to the development of more refined diagnostic approaches for suspected PE
• Demonstrated that incorporating clinical assessment, V/Q scanning, and DVT testing could reduce the need for pulmonary angiography from 72% to 33% of cases 3

Evolution of Diagnostic Criteria

• The original PIOPED criteria have been revised to improve the predictive values of lung scintigraphy 1
• Led to the development of a three-tier classification system: normal (excluding PE), high-probability (diagnostic of PE), and non-diagnostic scan 1

Modern Applications

• PIOPED II expanded on the original study by incorporating CT pulmonary angiography (CTPA) into diagnostic algorithms 4
• Demonstrated that V/Q scanning can still provide definitive results in approximately 73.5% of patients, making it an appropriate alternative when CTPA is contraindicated 5

Limitations and Pitfalls

• Only 28% of patients investigated for PE in the PIOPED study actually had the diagnosis confirmed 1
• Many patients (40%) had intermediate probability scans, requiring additional testing 2
• The original criteria were complex and had significant interobserver variability for intermediate categories 2
• Clinical probability assessment was challenging, with many patients unable to be clearly categorized as high or low risk 1

Modern Context

While CTPA has largely replaced V/Q scanning as the first-line imaging test for PE diagnosis in many centers, the PIOPED study's fundamental principles of integrating clinical probability with imaging results remain essential to modern diagnostic approaches. The study established the framework for current diagnostic algorithms that emphasize pre-test probability assessment and sequential testing strategies 6.