Diagnostic yield of sputum induction in patients with pleural tuberculosis at a tertiary care hospital in Karachi

OBJECTIVE : To evaluate the diagnostic yield of acid-fast bacilli (AFB) smear, culture for Mycobacterium tuberculosis and Xpert(R) MTB/RIF assay in induced sputum (IS) specimens in patients with pleural tuberculosis (TB). DESIGN: A total of 156 patients were evaluated at Jinnah Postgraduate Medical Centre, Karachi, Pakistan, from April 2016 to December 2017. Patients with exudative lymphocytic pleural effusions with normal lung parenchyma on chest radiography were included in the study: 102 were due to tuberculous and 54 due to non-tuberculous infections as diagnosed using thoracoscopic pleural biopsy. IS samples were sent for acid-fast bacilli (AFB) smear, AFB culture and Xpert assay. RESULT: In patients with a clinical diagnosis of TB, mycobacteria were detected in IS AFB smear in 7.8%, AFB culture in 21.6% and Xpert assay in 34.3% of cases. All sputum samples collected from patients with non-tuberculous aetiology were negative. CONCLUSION: Testing IS samples for M. tuberculosis provides another approach to diagnosing pleural TB, especially in settings in which invasive procedures are less accessible. Our study also emphasises the contagiousness of pleural TB, and the need to screen the household contacts of these patients and possible isolation of patients with pleural TB admitted to hospital.