What is the most likely diagnosis if sputum analysis shows mostly white blood cells?

When sputum analysis shows a predominance of white blood cells, it typically indicates an inflammatory process within the respiratory system. In the context of this scenario, pneumonia is characterized by the accumulation of leukocytes, particularly neutrophils, as the body responds to infection in the lungs.

Pneumonia can be caused by bacterial, viral, or fungal pathogens, and the immune response to these infections includes the recruitment of white blood cells to the site of infection, which can lead to purulent sputum. The presence of white blood cells in the sputum suggests that there is an ongoing infection or inflammation, which aligns with the diagnosis of pneumonia.

In contrast, conditions such as asthma usually present with sputum that may contain more eosinophils due to allergic inflammation, while chronic bronchitis might show a mixture of inflammatory cells but not predominantly white blood cells. Tumors can lead to sputum production but typically do not present with a significant increase in white blood cells unless there is a secondary infection associated with the tumor itself.

Thus, the finding of mostly white blood cells in the sputum is most consistent with pneumonia, making it the most likely diagnosis in this scenario.