The Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED)

Objectives:

To determine the sensitivities and specificities of ventillation/perfusion (V/Q) lung scans for acute pulmonary embolism (PE).

Background:

In 1983, reliable data on the incidence of pulmonary embolism in the adult population and in groups identified at risk were not available because the sensitivity and specificity of the diagnostic procedures had not been determined. Estimates suggested there were about half a million episodes of pulmonary embolism in hospitalized patients each year in the United States. Deaths attributable to pulmonary embolism would be expected in about one third of these patients if left untreated.

Subjects:

Eligible patients were 18 years of age or older without contraindications for pulmonary angiography, and for whom a request was made for a V/Q scan or a pulmonary angiogram. A total of 1,493 patients provided consent to participate in PIOPED and the analysis was conducted in a random sample of 933 patients. Patients suspected of pulmonary embolism underwent a ventilation-perfusion scan. Patients with an abnormal perfusion scan underwent angiography. All patients were followed for one year.

Conclusions:

Almost all patients with pulmonary embolism had abnormal scans of high, intermediate, or low probability, but so did most without pulmonary embolism. Only in a minority of patients did the clinical assessment combined with the V/Q scan interpretation improve the overall chance of reaching a correct diagnosis of acute PE. Although a high probability scan usually indicated the presence of PE, only a small number of patients with PE had a high probability scan. (JAMA 1990;263(20):2753-2759).