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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 diagnosis of active tuberculosis in patients who do not produce spontaneous sputum, or with smear-negative spontaneous samples.


METHODS
Induced sputum was examined with fluorescent microscopy, two amplification methods (PCR Amplicor MTB, and MTD2), and 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.


RESULTS
A total of 1115 sputum inductions performed in 500 patients without adverse events yielded an adequate specimen in 1113 (99.8%), and microbiological confirmation in 43 of 44 (98%) culture-positive active TB 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, 81% and 91% for two, 91% and 99% for three, and 98% and 100% for four induced samples. Yield of PCR also increased with the greater number of induced samples tested.


CONCLUSIONS
Repeated sputum induction could considerably improve diagnostic accuracy for pulmonary TB.