Yield of smear, culture and amplification tests from repeated sputum induction for the diagnosis of pulmonary tuberculosis

OBJECTIVES: To assess the yield of repeated sputum induction for the diagno sis of active tuberculosis in patients who do not produce spontaneous sputu m, or with smear-negative spontaneous samples. METHODS: Induced sputum was examined with fluorescent microscopy, two ampli fication methods (PCR Amplicor MTB, and MTD2), and cultured for mycobacteri a using liquid (Bactec 12B) and Lowenstein-Jensen media. Bronchoscopy and c ollection of other specimens were performed at the discretion of the treati ng physician. RESULTS: A total of 1115 sputum inductions performed in 500 patients withou t adverse events yielded an adequate specimen in 1113 (99.8%), and microbio logical confirmation in 43 of 44 (98%) culture-positive active TB cases. Yi eld increased with repeated sputum induction. The cumulative yield for acid -fast bacilli smear and mycobacterial culture was 64% and 70% respectively for one, 81% and 91%for two, 91% and 99% for three, and 98% and 100% for fo ur induced samples. Yield of PCR also increased with the greater number of induced samples tested. CONCLUSIONS: Repeated sputum induction could considerably improve diagnosti c accuracy for pulmonary TB.