Children with tuberculous Pleural Effusion (PE) usually present with fever, chest pain, anorexia and weight loss. While more prolonged duration symptoms may make TB aetiology more likely, TB PE can often present acutely. TB effusion can present with high-grade fever. The clinical examination would reveal signs of effusion (decreased air entry with dull percussion).

The presence of effusion can be confirmed by chest imaging (USG or chest radiograph). Pleural diseases are best imaged with a USG, and its benefit relates to establishing the presence and extent of PE and not for establishing an etiological diagnosis. Nevertheless, CT Chest makes little contribution to suggest aetiology. Pleural fluid aspiration should always be performed, and the aspirate should be sent for biochemical, cytological and smear examination by Ziehl-Neelsen (ZN) stain to confirm the diagnosis. In the absence of a pleural fluid examination, it is usually not possible to infer any aetiology based on radiology alone. Typically, a tubercular effusion fluid is straw-coloured (pus, if aspirated, is very rarely due to TB aetiology) has large numbers of cells (in hundreds; predominantly mononuclear), with high proteins (>3g/dL). Moreover, the high protein content of the exudative effusion in tuberculosis causes it to form a cobweb on standing. However, the yield of NAAT in tubercular pleural effusion is low. Induced sputum/GA should always be tested for M.tb as about a quarter of the children with PE, GA or IS were positive on culture. On the other hand, the M.tb detection in Pleural fluid, by culture or NAAT, is about 5%. Similarly, positive skin test for TB is supportive and not diagnostic. Blood count within the normal range makes empyema or a complicated para-pneumonic effusion less likely. ESR has no role in establishing the aetiological diagnosis.

Although Adenosine Deaminase (ADA) has been used extensively to diagnose TB effusion in adults, its utility in children appears limited. Studies among adults have compared TB effusions with malignant effusions and have found it to be a good marker. However, very few studies compare TB effusion with parapneumonic effusions, which is the commonest other cause in children. Limited data suggest a significant overlap between the ADA values in TB effusion and pyogenic effusions, and therefore, it is not recommended to be used for children.

A pleural biopsy may be performed in unclear situations using Cope’s or Abraham’s pleural biopsy needle. The pleural tissue can be subjected to histopathology, ZN staining and MGIT cultures. The findings of granulomas with caseous necrotic tissue in the pleural biopsy makes the diagnosis of tuberculosis highly probable. The yield of pleural biopsy is more than 80%. In most circumstances, the diagnosis can be made by a combination of a long history, a non-sick child, an exudative (not pus) lymphocytic effusion. A skin test for TB may be another supportive clue.