Diagnostic yield of pleural fluid cytology in malignant effusions: an Australian tertiary centre experience

Background: Timely diagnosis of malignant pleural effusions is critical to guide prognosis and management decisions. Cytological analysis of pleural fluid has been the firstline diagnostic test for many decades, with highly variable reported sensitivities of 40-90%. Its diagnostic accuracy in modern practice in Australia needs to be understood. Aims: To determine the diagnostic yield of pleural fluid cytology for the detection of malignant pleural effusions and to determine the aetiologies of pleural effusions at our centre. Methods: The study involved the retrospective chart review of all pleural fluid samples submitted for cytological analysis at a tertiary referral centre in Melbourne, Australia, over a 12-month period. Aetiology of all effusions was determined, and sensitivity, specificity, negative predictive value and diagnostic accuracy for the detection of malignant pleural effusions were calculated. We also examined diagnostic yield based on tumour cell type. Results: Of the 153 cases analysed, 61 (39.9%) were malignant. Lung cancers accounted for 44.3% of malignant effusions, followed by mesothelioma (18%), ovarian carcinoma (11.5%) and lymphoma (8.2%). The commonest single causes of a benign effusion were cardiac (16.3%) and parapneumonic (13%). Sensitivity for diagnosis of malignant effusions was 67.2% overall, but 87.9% for adenocarcinomas and only 45.5% for mesothelioma. Conclusion: Tumour type is an important determinant of pleural fluid cytology diagnostic yield. Cytology has good sensitivity and specificity for the diagnosis of adenocarcinoma, but if another tumour type is suspected, particularly mesothelioma, clinicians should be aware of the limitations.