Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP upright portable chest radiograph was provided . There is increased nodular opacity in the left lung base concerning for pneumonia . The right lung is clear . Heart size is difficult to assess . Mediastinal contour is stable . No large effusion or pneumothorax is seen . Bony structures appear intact , though degenerative changes at the glenohumeral joint is noted bilaterally .
    OUTPUT:
    
Subtle nodular opacity at the left lung base is concerning for pneumonia .