Prospective Investigation of Pulmonary Embolism Diagnosis
PIOPED trial design and results
Design
Prospective diagnostic accuracy study with angiographic reference standard
Treatment
Ventilation-perfusion lung scanning
Control
Pulmonary angiography as reference standard
Population
931 patients underwent scintigraphy and 755 underwent pulmonary angiography, of whom 251 (33%) had pulmonary embolism
Follow-up
Diagnostic study with follow-up
Primary endpoint
Sensitivity and specificity of ventilation-perfusion scanning
Result
Almost all patients with pulmonary embolism had an abnormal scan, but so did most without it (sensitivity 98%, specificity 10%). Of 116 with high-probability scans and definitive angiograms, 102 (88%) had PE, but only a minority of those with PE had high-probability scans (sensitivity 41%, specificity 97%). Of 322 with intermediate-probability scans, 105 (33%) had PE. Around 12% of those with low-probability scans had PE.
Secondary endpoints
Predictive value of scan categories combined with clinical assessment
Clinical assessment combined with the ventilation/perfusion scan established the diagnosis or exclusion of pulmonary embolism only for a minority of patients — those with clear and concordant clinical and ventilation/perfusion scan findings.
The trial authors, in the published abstract
How it has aged
The trial that taught a generation that a scan reported as low probability still carries a 12% chance of pulmonary embolism. It made pretest probability compulsory rather than optional, and everything since — YEARS, PEGeD, ADJUST-PE — builds on that lesson.
Publications
Value of the ventilation/perfusion scan in acute pulmonary embolism. Results of the prospective investigation of pulmonary embolism diagnosis (PIOPED)
Value of the ventilation/perfusion scan in acute pulmonary embolism. Results of the prospective investigation of pulmonary embolism diagnosis (PIOPED). JAMA 1990 May 23-30;263(20):2753-9.
High-probability scans were 97% specific but only 41% sensitive
12% of low-probability scans still had pulmonary embolism
Diagnosis established only when clinical assessment and scan agreed