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

Yield of smear, culture and amplification tests from repeated sputum induction for the diagnosis of pulmonary tuberculosis. Int J Tubercul Lung Dis 2001;5:855–60. Al Zahrani K, Al Jahdali H, Poirier L, Rene P, Menzies D. Montreal Chest Institute, McGill University, Quebec, Canada. Comments: This study evaluated the yield of repeated sputum induction for the diagnosis of active tuberculosis in patients who could not produce spontaneous sputum or who had smear-negative spontaneous samples. Induced sputum was examined with fluorescent microscopy, two amplification methods (PCR Amplicor MTB and MTD2), and were cultured for mycobacteria using liquid (Bactec 12B) and Lowenstein–Jensen media. Bronchoscopy and collection of other specimens were performed at the discretion of the treating physician. A total of 1,115 sputum inductions performed in 500 patients without adverse events yielded an adequate specimen in 1,113 (99.8%), and microbiologic confirmation in 43 of 44 (98%) culture-positive active tuberculosis cases. Yield increased with repeated sputum induction. The cumulative yield for acid-fast bacilli smear and mycobacterial culture was 64% and 70% respectively for one sample, 81% and 91% for two samples, 91% and 99% for three samples, and 98% and 100% for four induced samples. Yield of the polymerase chain reaction also increased with the greater number of induced samples tested. The authors conclude that repeated sputum induction could improve considerably the diagnostic accuracy for pulmonary tuberculosis. This study is important in that it reminds us to consider repeated sputum studies in patients suspected of having tuberculosis.