Diagnosing pulmonary tuberculosis by pooling induced sputum

Introduction: Early diagnosis and treatment of pulmonary tuberculosis (PTB) remains fundamental in reducing transmissions and death. Sputum induction is recommended for the diagnosis of pulmonary tuberculosis (PTB) in patients who are unable to expectorate or smear negative. Objective: The aim of this study was to evaluate the diagnostic accuracy of pooling two induced sputum specimens into one microbiological test over a single day for the diagnosis of PTB. Methods: We prospectively enrolled consecutive hospitalized adults with suspected PTB from 2009-2016. Two induced sputum specimens were obtained on the same day and pooled together for AFB smear, culture and Xpert MTB/RIF testing. The final diagnosis of PTB was based on a positive culture from any respiratory specimen. All patients were followed up for 3 months. Results: Of 420 patients, 86(20.5%) were diagnosed with PTB based on a positive respiratory culture. The sensitivity, specificity, positive and negative predictive values for pooled induced sputum were 98.8% (CI 93.7-100%), 100% (CI 98.9-100%) and 100% (94.6-100%) and 99.7% (CI 98.1-100%) respectively. Xpert MTB/RIF in pooled induced sputum was positive in 88.4% of the PTB patients. Conclusion: In the diagnosis of PTB, testing two induced sputum specimens which were pooled together for one microbiological testing process may be comparable to repeat testing.