The accuracy of the clinical diagnosis of new-onset idiopathic pulmonary fibrosis and other interstitial lung disease: A prospective study.

STUDY OBJECTIVES Presently, surgical (open or thoracoscopic) lung biopsy (SLB) is the gold standard for the diagnosis of new-onset idiopathic pulmonary fibrosis (IPF) and other interstitial lung diseases (ILDs). The accuracy of a clinical diagnosis of IPF and other subsets of ILD has never been established in prospective studies. We investigated the accuracy and validity of a clinical diagnosis of IPF and ILD other than IPF. DESIGN Prospective, independent evaluation of patients and clinical data by an ILD expert, of chest radiographic and high-resolution computed tomography (HRCT) features by a chest radiologist, and of histologic features of lung biopsy by a pulmonary pathologist in consecutive patients referred for a diagnostic evaluation of ILD. SETTING Tertiary university medical center with recognized expertise in management of ILD. PATIENTS Community patients referred for further definitive diagnostic evaluation of new-onset, untreated nonspecific ILD. INTERVENTION By comparing the histologic features of SLB in 59 patients consecutively referred for further diagnostic evaluation of new-onset ILD with the clinical and radiologic diagnoses, we determined the sensitivity and specificity of clinical diagnosis and radiologic diagnosis (based on chest radiograph and HRCT features alone) of IPF and ILD other than IPF. A specific clinical diagnosis was independently made by the ILD expert after a thorough clinical assessment that included evaluation of an HRCT scan and bronchoscopic findings. The chest radiographs and HRCT scans were separately reviewed by the chest radiologist, who made a radiologic diagnosis independently. All patients underwent SLB within a month of preoperative "clinical" diagnosis. The clinician's and radiologist's diagnoses were then compared with the gold standard of histologic diagnosis. MEASUREMENTS AND RESULTS Prior to the clinical evaluation at our center, 85% of patients who underwent SLB had nondiagnostic transbronchial biopsy. The diagnosis of IPF and ILD other than IPF was accurately made by clinical features alone in 62% of cases. The correct radiographic diagnosis of non-IPF ILD was made in 58% of the cases. The sensitivity and specificity of the clinical diagnosis of ILD other than IPF were 88.8% and 40%, respectively. The sensitivity and specificity of the radiographic diagnosis of ILD other than IPF were 59% and 40%, respectively. However, the sensitivity and specificity of the diagnosis of IPF on clinical grounds were 62% and 97%, respectively. The sensitivity and specificity of the radiologic diagnosis of IPF were 78.5% and 90%, respectively. CONCLUSIONS In a center with recognized expertise in the management of ILD, the specificity of diagnosis of new-onset IPF based on a thorough clinical assessment or HRCT features alone is very high (97% and 90%, respectively), but the sensitivity is low (62% and 78.5%, respectively). Thus, not all patients with new-onset IPF require SLB for diagnosis, but a diagnosis of IPF will be missed in nearly one third of new-onset IPF cases despite evaluation by experts. The relatively low sensitivity and specificity of the diagnosis of ILD other than IPF also emphasizes that an SLB is indicated in patients with ILD in whom the diagnosis is unclear.