What is the first investigation to be done for suspected interstitial lung disease patient?

ILD may be first suspected on basis of abnormal CXR. Findings seen are:- 1. Bibasilar reticular pattern. 2. Nodular opacities. 3. Honeycombing. Subsequently HRCT is done for assessment of the extent of disease, mediastinal adenopathy and determining the site for biopsy. Lung biopsy is the most effective method for confirming the diagnosis of ILD . MDCT is used in pulmonary embolism. Hence choice C is ruled out. Spirometry findings show a restrictive pattern but in some cases, the obstructive pattern is seen. Hence choice D is ruled out.