Repeated measurements of different clinical and physiological parameters are believed to be useful in assessing the clinical course of IPF. Assessment of dyspnea and using an established clinical scale for rating the impact of dyspnea on activities are standard for IIPs evaluation.  Lung volumes, DLCO, resting arterial blood gases, cardiopulmonary exercise testing with measurement of gas exchange, HRCT lung scans are our current tools for diagnosing and monitoring idiopathic<unk>  pneumonia. Physiologic testings have been used to determine the current functional lung capacity. Studies have shown that conventional lung function tests by spirometry have more precision in prognosis of patients with IPF, while extensive tests like gas exchange measurements at rest and exercise do not add additional information to make the prognostic or treatment evaluation more precise. .
The diagnosis of IIPs is dynamic as it depends on multidisciplinary approach among different specialists. The histological patterns identified by the pathologists give better distinguishing patterns than imaging patterns identified by radiologists. Clinical-radiological-pathological diagnosis (CRP diagnosis) is rely on histopathological findings as a very informative tool to reach the definitive diagnosis. Also the practice of delaying the biopsy till the patient starts to deteriorate clinically and radiologically is not helpful as it delays the diagnosis and reduce the likelihood of the disease to be accurately identified. 
However the surgical biopsy is important for classification and confident CRP diagnosis, it is not always necessary to reach diagnosis, especially in the cases where there is a typical clinical-radiological picture of UIP/IPF. The diagnostic criteria for idiopathic pulmonary fibrosis without a  surgical biopsy adopted by AT/ERS.
Exclusion of other known causes of ILD, such as certain drug toxicities, environmental exposures, and connective tissue diseases
Transbronchial lung biopsy/BAL showing no features to support an alternative diagnosis
Restrictive pulmonary function studies (reduced VC, often with an increased FEV1/FVC ratio) and impaired gas exchange (increased P[A-a]O2, decreased PaO2 with rest or exercise or decreased DLCO)
HRCT scans with bibasilar reticular abnormalities with minimal ground-glass opacities
Age > 50 yr 
Insidious onset of unexplained dyspnea on exertion 
Duration illness > 3 mo 
Bibasilar, inspiratory crackles
adopted from the joint statement of American Thoracic Society.
In the immunocompetent adult, the presence of all of the major diagnostic criteria + at least three of the four minor criteria increases the likelihood of a correct clinical diagnosis of IPF.
Idiopathic interstitial pneumonia Diagnostic criteria
Idiopathic interstitial pneumonia diagnostic criteria
Eosinophilic pneumonia diagnostic criteria
Eosinophilic pneumonia classification
Idiopathic interstitial pneumonia classification
Hypersensitivity pneumonitis classification
Pneumoconiosis diagnostic criteria
Aspergillosis diagnostic criteria