Doyle and colleagues [1] raise important points in their report on the necessity of chest radiography after thoracentesis. However, I think that this report may be misleading. Chest radiography is done after thoracentesis for reasons other than determining whether a pneumothorax has occurred.

I often obtain a chest radiograph after evacuation of a large pleural effusion, particularly if I believe that I have removed most of the fluid. The evacuation of fluid may reveal a lung mass that had been masked by the effusion. Removal of pleural fluid can occasionally lead to a condition in which the lung does not completely expand to occupy the chest cavity, particularly in the setting of obstructive lung lesions. The post-thoracentesis chest radiograph has been helpful in showing this phenomenon. A post-thoracentesis chest radiograph helps establish a baseline with which subsequent chest radiographs can be compared to help evaluate the speed with which pleural fluid is reaccumulating.

I agree wholeheartedly that in many cases, the absence of pneumothorax after thoracentesis can be predicted with good accuracy without immediate chest radiography. However, physicians should not infer that radiography of the chest has no value after thoracentesis, particularly if a large volume has been evacuated.