Measures of clinical efficacy. III. The value of the lung scan in the evaluation of young patients with pleuritic chest pain.

The usefulness of various modalities in evaluating pleuritic pain in young patients and in isolating cases of pulmonary embolism was assessed using likelihood ratios and the receiver operating characteristic (ROC) curve. History and physical, laboratory, and radiographic finding were used disjunctively to establish an ROC curve. The percentage of patients found to have pulmonary embolism increased monotonically with certain critical pieces of diagnostic data. For example, a history and physical examination alone detected 80% of patients with pulmonary embolism; a chest radiograph raised the percentage to 95%; and the addition of a lung scan increased the percentage to 100%. Thus, with proper interpretation of clinical and radiographic data, the lung scan has only a marginal impact upon the sensitivity with which pulmonary embolism is detected. Its major value is an increased specificity in the diagnosis of pulmonary embolism.