Sensitivity and Specificity of Perfusion Scintigraphy Combined with Chest Radiography for Acute Pulmonary Embolism in PIOPED II

We used the archived Prospective Investigation of Pulmonary Embolism Diagnosis I I (ROPED II) data and images to test the hypothesis that reading perfusion scans with chest radiographs but without ventilation scans, and categorizing the perfusion scan as pulmonary embolism (PE) present or PE absent, can result in clinically useful sensitivity and specificity in most patients. Methods: Patients recruited into ROPED II were eligible for the present study if they had a CT angiography (CTA) or digital subtraction angiography (DSA) diagnosis, an interpretable perfusion scan and chest radiographs, and a Wells' score. Four readers reinterpreted the perfusion scans and chest radiographs of eligible patients. Two readers used the modified PIOPED II criteria and 2 used the Prospective Investigative Study of Pulmonary Embolism Diagnosis (PISAPED) criteria. The chest radiographs were read as normal/near normal, abnormal, or nondiagnostic, and the perfusion scans were read as PE present, PE absent, or nondiagnostic. The primary analysis used a composite reference standard: the ROPED II DSA result or, if there was no definitive DSA result, CTA results that were concordant with the Wells' score as defined in ROPED II (CTA positive and Wells' score > 2, or CTA negative and Wells' score < 6). Results: The prevalence of PE in the sample was 169 of 889 (19%). Using the modified ROPED II criteria, the sensitivity of a PE present perfusion scan was 84.9% (95% confidence interval [CI], 80.1%-88.8%), and the specificity of PE absent was 92.7% (95% CI, 91.1%-94.1%), excluding nondiagnostic results, which occurred in 20.6% (95% CI, 18.8%-22.5%). Using PISAPED criteria, the sensitivity of a PE present perfusion scan was 80.4% (95% CI, 75.9%-84.3%) and the specificity of PE absent was 96.6% (95% CI, 95.5%-97.4%), whereas the proportion of patients with nondiagnostic scans was 0% (95% CI, 0.0%-0.2%). Conclusion: Perfusion scintigraphy combined with chest radiography can provide diagnostic accuracy similar to both CTA and ventilation-perfusion scintigraphy, at lower cost and with lower radiation dose. With modified ROPED II criteria, a higher proportion of scans were nondiagnostic than with CTA, and with PISAPED criteria none were nondiagnostic.