Role of Demonstration of Acid Fast Bacilli in Pleural Effusions - A one year study

Pleural effusion results from excess fluid production or decreased absorption or both. Tuberculous (TB) pleural effusion is one of the most common forms of extrapulmonary TB. The present study included 158 cases of pleural effusions which were processed and stained with Giemsa, Papanicolaou stain (PAP), Hematoxylin and Eosin stain (H&E) and Ziehl–Neelsen (ZN) stain for Acid fast bacilli (AFB). All samples were categorized according to Indian Academy of Cytopathologists (IAC) guidelines 2019. Out of 158 cases, only one case showed positivity for acid-fast bacilli (AFB), which is consistent with the known low detection rate of AFB on microscopy. An exception to this low detection rate has been reported in patients with Human Immunodeficiency Virus (HIV) infection and in cases of tuberculous empyema, where previous studies have shown a higher yield of acid-fast bacilli on pleural fluid microscopy, with AFB positivity reported in more than 20% of such cases. However, cytological examination plays an important supportive role in the diagnosis of tuberculous pleural effusion by identifying lymphocyte-predominant effusions, and demonstration of acid-fast bacilli on Ziehl–Neelsen staining, although infrequent, provides confirmatory evidence. Hence, cytological examination, when interpreted alongside clinical, radiological, and microbiological findings, contributes to improving the diagnostic accuracy of tuberculous pleural effusion.