Diagnostic accuracy of exudative pleural fluid cytology with the correlation of gene xpert in Tuberculosis

Background: Pleural fluid is categorised as either transudate or exudate based on modified Light’s criteria. Pleural effusion is classified as an exudative effusion if at least one of the criteria is met. Pleural fluid protein/serum protein ratio of greater than 0.5. Pleural fluid lactate dehydrogenase (LDH)/serum LDH ratio of greater than 0.6. Pleural fluid lactate dehydrogenase (LDH) is greater than 2/3rd of the upper limit of normal value for serum lactate dehydrogenase (LDH). Materials and Methods: A prospective study was conducted over 21 months at Nalanda Medical College and Hospital, Patna. Pleural fluid samples from 130 patients were collected from various departments. Each sample underwent physical, chemical, cytological, and microbiological examinations, including Ziehl-Neelsen staining for acid-fast Bacillus and Gene Xpert testing for Mycobacterium tuberculosis. Demographic information, clinical history, and laboratory findings were documented. Patients with positive Gene Xpert results were monitored on anti-TB treatment for six months, while Gene Xpert-negative patients received a two-week antibiotic regimen. Statistical analyses, including sensitivity, specificity, and predictive values, were calculated. Results: Out of 130 pleural fluid samples, 84% were exudates, with a higher prevalence in males (64.55%) and patients aged 21-30 years. Suspected clinical diagnoses included tuberculosis (77.36%), pneumonia (18.18%), and malignancy (5.04%). WBC counts were predominantly in the range of 600-1000 cells/µL, and protein levels were above 3 gm/dL in all exudative cases. Cytology showed a predominance of lymphocytes in suspected tuberculosis cases, with a mean of 83%. Gene Xpert detected Mycobacterium tuberculosis in 39.58% of cases, with high sensitivity (86.49%) and specificity (46.43%) for cytological diagnosis relative to Gene Xpert, achieving a diagnostic accuracy of 62.37%. Lymphocyte predominance was significantly associated with tuberculosis (p < 0.001). Conclusion: Pleural fluid cytology, combined with advanced molecular techniques like Gene Xpert, provides an effective, minimally invasive diagnostic approach for tuberculosis, particularly in resource-limited settings. Cytology demonstrates high sensitivity and negative predictive value, making it valuable in diagnosing tuberculosis and distinguishing it from other causes of pleural effusion.