A Comparative Study of Induced Sputum and Bronchial Washings in Diagnosing Sputum Smear Negative Pulmonary...

Tuberculosis is one of the most important public health problem worldwide. Detecting patients with active pulmonary Koch's disease is an important component of tuberculosis control programs. However, at times in patients even with a compatible clinical picture, sputum smears do not reveal acid-fast bacilli and smear-negative pulmonary tuberculosis remains a common problem.

The present study is aimed to compare the results of induced sputum and bronchial washings smear in patients suspected to have sputum smear negative pulmonary tuberculosis.

A prospective study conducted from August 2014 to July 2015, comprising 120 patients fulfilling study criteria. Patients with respiratory symptoms and chest roentgenogram suspicious of pulmonary tuberculosis with no previous history of anti-tuberculosis treatment and two spontaneous sputum smear samples negative for acid fast bacilli were included. Patients with active haemoptysis and sputum positive were excluded from the study. Sputum induction was done by using 5-10 ml of 3% hypertonic saline through ultrasonic nebulizer taking safety precautions. All the patient underwent fibreoptic bronchoscopy after six hours fasting on the same day. About 20 ml of normal saline instilled into the suspected pathology area and washings were taken with gentle suction. The sample processing and fluorescent staining for acid fast bacilli was done in a designated microscopy lab.

Out of 120 sputum smear negative pulmonary tuberculosis patients, induced sputum smear examination detected acid fast bacilli in 76 patients (63.3%) and acid fast bacilli detected from bronchial washings in 94 patients (78.3%). Smear positivity was higher in cavitary and infiltrative lesions as compared to consolidation and infrahilar pattern disease.

Even though both induced sputum and bronchial washings procedures were valuable for the diagnosis of sputum smear negative, sputum induction with hypertonic saline should be the initial procedure of choice, which can be repeated twice / thrice in a day or two consecutive days. If the patient still remains induced sputum smear negative and if the clinical probability of tuberculosis is high, starting anti-tuberculosis treatment and closely monitoring patient and reserving bronchoscopy to those patients who do not improve and to exclude alternative diagnosis seems to be a practically useful approach.