Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP upright portable chest radiograph is obtained . The lung volumes are somewhat low . There is subtle poorly defined opacity at the left lung base , which could represent a very early pneumonia . No pleural effusion or pneumothorax is seen . Two surgical clips project over the right lung apex . The heart and mediastinal contour appears normal . Bony structures are intact . No free air below the right hemidiaphragm .
    OUTPUT:
    
Subtle opacity at the left lung base could represent early pneumonia .