Which type of cells should be reported when many large cells with basophilic cytoplasm are seen in a slide from peritoneal fluid?

When examining peritoneal fluid and observing many large cells with basophilic cytoplasm, the correct response is to report these as mesothelial cells. Mesothelial cells line the peritoneal cavity and are characterized by their large size and basophilic (blue-staining) cytoplasm, which is indicative of active protein synthesis and reflects the characteristics of their secretory function.

These cells often appear in clumps or sheets and can adopt a varied morphology but generally maintain their basophilia due to the presence of ribosomes and rough endoplasmic reticulum involved in producing fluid components. In the context of peritoneal fluid, a significant presence of mesothelial cells typically suggests a reactive process related to irritation or inflammation rather than malignancy, although in certain circumstances, elevated mesothelial cells can be encountered in neoplastic conditions.

Noting this context, the identification of mesothelial cells can help differentiate between benign and malignant effusions, guiding further diagnostic processes. Other cells such as large lymphocytes or macrophages present in peritoneal fluid would exhibit different characteristics and staining patterns.