EC Pulmonology and Respiratory Medicine

Tuberculous pleural effusion (TPE) poses significant diagnostic difficulties, especially in regions where tuberculosis (TB) is prevalent. In this prospective study, we evaluated the diagnostic performance of the Lactate Dehydrogenase (LDH) to Adenosine Deaminase (ADA) ratio as a tool for identifying TPE among patients presenting with suspected pleural TB. The practicality and affordability of LDH and ADA measurements in pleural fluid make this approach particularly valuable for resource-limited healthcare environments such as India.

A total of 66 patients with exudative, lymphocyte-predominant pleural effusions and a high pretest probability of TB were enrolled, with an equal number exhibiting ADA levels above and below 40 IU/L. Etiological diagnoses incorporated clinical history, radiological findings, and biochemical and cytological assessment of pleural fluid. The mean participant age was 48.3 years, and male patients predominated (72.7%). Frequent presenting symptoms included cough, breathlessness, fever, chest pain, and other constitutional complaints. Common comorbidities among participants were systemic hypertension, type 2 diabetes mellitus, and chronic kidney disease.

Biochemical analysis of pleural fluid revealed mean levels of glucose at 80.86 mg/dl, protein at 6.24 g/dl, ADA at 46.14 IU/l, and LDH at 817.09 U/l. ADA demonstrated robust diagnostic performance with an area under curve (AUC) of 0.940. Setting an optimal cutoff of 16.89 IU/l provided 86.7% sensitivity and 88.9% specificity for detecting TB-related effusions.

In summary, pleural fluid ADA and LDH are highly sensitive and specific in distinguishing exudative from transudative effusions. The LDH/ADA ratio serves a pivotal role in differentiating TPE from other exudative etiologies such as parapneumonic or malignant effusions, especially given TPE’s tendency for intermediate ADA values due to its paucibacillary nature. Relying on the LDH/ADA ratio can streamline diagnostics and reduce dependence on simultaneous testing, which is particularly advantageous in resource-limited settings. Optimizing these diagnostics can facilitate earlier treatment, thereby improving patient outcomes and reducing morbidity associated with TPE.

 Keywords: Extra Pulmonary Tuberculosis; Exudative Pleural Effusion; Lactate Dehydrogenase; Adenosine Deaminase; Tuberculous Pleural Effusion; Co Morbidities

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