[2026-01-26] Pleural Fluid Volume for Cytological Diagnosis of Malignancy: How Much Is Optimum

Abstract

Background: Pleural fluid cytology is essential for evaluating effusions and detecting atypical and malignant cells. However, the optimal fluid volume for accurate diagnosis remains unclear.

Objective: To determine the optimal pleural fluid volume for detecting atypical to malignant cells by analyzing diagnostic yield across different volume groups.

Methods: This retrospective study analyzed pleural fluid samples collected between 2020 and 2021, correlating to cases with confirmed malignancy in pleural cavities. Samples were categorized into volume groups and classified using the International System for Serous Fluid Cytopathology: nondiagnostic (ND), negative for malignancy (NFM), atypia of undetermined significance (AUS), suspicious for malignancy (SFM), and malignant (MAL).

Results: Of 1794 pleural fluid samples, the detection rates of atypical to malignant cells in the samples were < 25 mL (35.87%), 25-49 mL (40.77%), 50-74 mL (45.38%), 75-99 mL (37.89%), 100-249 mL (29.67%), 250-499 mL (21.99%), and ³ 500 mL (40.97%). Considering the samples with evidence of pleural involvement by malignancy (n = 497), detection rates of atypical to malignant cells in the samples were < 25 mL (83.72%), 25-49 mL (91.67%), 50-74 mL (90.41%), 75-99 mL (93.33%), 100-249 mL (72.06%), 250-499 mL (44.17%), and ³ 500 mL (82.14%). The proportion of AUS and SFM categories among the atypical and malignant samples were low (< 20%) in the 50-74 mL and 75-99 mL volume groups.

Conclusions: Intermediate volumes (50-100 mL) provide adequate cellular material while maintaining manageable sample processing. Implementing this volume range in clinical practice may enhance diagnostic accuracy.