Diagnostic Yield of Induced Sputum and Bronchial Aspirate in Sputum Smear Negative Pulmonary Tuberculosis Patients

Researche Article

Abstract

Introduction: Tuberculosis is one of the most important public health problem worldwide, detecting patients with active pulmonary tuberculosis is an important disease control measure. Diagnosing sputum smear negative pulmonary tuberculosis is challenging and in this study, an attempt is made to compare the diagnostic yield of smear and CBNAAT with culture in smear negative PTB patients.
Aims and Objectives: 1. To determine the diagnostic yield of CBNAAT, AFB smear, AFB Culture on induced sputum and bronchial aspirate 2. To evaluate the sensitivity, specificity, PPV, NPV of CBNAAT in sputum negative respiratory samples as compared with AFB culture.
Methods: This is a prospective observational study done in the department of Pulmonary Medicine, Goa Medical College, from October 2016 to August 2018. All patients of suspected Tuberculosis based on clinical and radiological diagnosis underwent sputum induction and flexible video-bronchoscopy as per standard protocol. Our study had a different and unique approach where smear negative PTB patients were subjected to sputum induction procedure initially, those which were positive on induced-sputum CBNAAT were diagnosed as PTB and started on treatment. However cases which were induced-sputum CBNAAT negative were subjected to fibreoptic bronchoscopy. The bronchial aspirate from the involved segment was collected and sent for smear, CBNAAT and Culture.
Results: The total number of patients included were 202 cases. Males- 64.9%, females- 35.1%. The most common symptom was cough with expectoration in 99% individuals. Multiple heterogenous opacities on chest radiography seen in 65.3% of cases. The overall diagnostic yield of AFB smear, CBNAAT and AFB Culture were 41/202(20.29%), 134/202(66.33%) and 144/202(71.28%) respectively. The sensivity, specificity, PPV and NPV of induced sputum smear was 28.5%, 98.7%, 96.7% and 76.7% and that of Induced sputum CBNAAT was 84.2%, 98.0%, 94.1% and 94.9% respectively. The sensitivity, specificity, PPV and NPV of bronchial aspirate smear was 26.31%, 100%, 100% and 69.2% and that of BA CBNAAT was 84.6%, 98.4%, 97% and 91.1% respectively. In this study around 17 patients were culture positive and CBNAAT negative, among 17 cases 3 patients(17.64%) were diagnosed to have Non tuberculous mycobacterial pulmonary disease on AFB culture.
Conclusions: Our study shows that CBNAAT has high sensitivity and specificity in diagnosing smear negative pulmonary tuberculosis than AFB smear microscopy as comparable to AFB culture which is gold standard. Hence all smear negative patients should be evaluated with CBNAAT and also helps in diagnosing RIFAMPICIN resistant Tuberculosis. Use of procedures like induced sputum further increases yield of diagnosis and is a powerful tool in diagnosis of smear negative PTB suspects reserving invasive procedure like Fibreoptic bronchoscopy for undiagnosed cases.