Low Adenosine Deaminase (ADA) Does Not Exclude Tuberculosis: A Case of Loculated Pleural Effusion Diagnosed by a Medical Thoracoscopic Pleural Biopsy

Tubercular pleural effusion is a common cause of exudative pleural effusion, particularly in endemic regions, and adenosine deaminase (ADA) is widely used as a supportive diagnostic marker. However, lower-than-expected ADA levels can lead to diagnostic uncertainty. We report a 21-year-old male who presented with prolonged fever, weight loss, and dry cough. He was initially managed as a case of parapneumonic effusion due to lymphocytic exudative pleural fluid with low ADA levels. Persistent symptoms and imaging findings of multiple loculated pleural collections with associated lung collapse prompted further evaluation. Medical thoracoscopy revealed septations and nodular pleural lesions, and targeted biopsy demonstrated chronic granulomatous inflammation consistent with tuberculosis. This case underscores the limitations of interpreting ADA in isolation and highlights the importance of integrating clinical, radiological, and histopathological findings. Early use of a thoracoscopic pleural biopsy plays a key role in establishing diagnosis in complex or inconclusive pleural effusions.