Risk Stratification of Pleural Fluid Cytology Based on the International System for Reporting Serous Fluid Cytology in a Tertiary Care Centre

Background: The International Academy of Cytology and the American Society of Cytopathology proposed the international system for reporting serous fluid cytology (TISRSFC) in 2019 to form uniform reporting terminologies for fluid cytology. This system defines a spectrum of diagnostic categories to be used in daily clinical practice. Fluid cytology is a widely accepted, cost-effective, minimally invasive earliest diagnostic method for the investigation that aids management decisions. The present study aims to reclassify pleural fluid cytology and calculate the risk of malignancy (ROM) for each diagnostic category. Material and Methods: It is a retrospective 2 years observational study comprising 690 pleural fluid specimens. Retrospective reviews were performed, and cases were reclassified into five categories as per TISRSFC. Immunohistochemistry was applied whenever needed. Cytological diagnosis was correlated with respective histopathology and/or clinical and/or radiological diagnosis. ROM was calculated for all diagnostic categories. Results: In the present study of 690 cases, 7.97% were non-diagnostic (ND), 84.1% cases were negative for malignancy (NFM), 0.87% were atypia of undetermined significance (AUS), 1.16% were suspicious for malignancy (SFM), and 5.94% were malignant (MAL). Cell blocks were prepared in 33 (4.8%) cases and immunohistochemistry was applied in 7 cases. The commonest site for pleural fluid metastasis was the lungs, accounting for 4.64% (32/690) cases. Further, ROM was calculated for all diagnostic categories as follows: (1) ND: 30.9%, (2) NFM: 12.9%, (3) AUS: 100%, (4) SFM: 100%, and (5) MAL: 90.2%. Conclusion: Cytological examination of pleural fluids is an accurate, prompt, and affordable technique. This standardized ISRSFC reporting system will maintain uniformity and reproducibility in reporting, leading to improved clinical decision-making of pleural fluids.