The validity of acid-fast smears of gastric aspirates as an indicator of pulmonary tuberculosis

SETTING: A tuberculosis referral hospital in Canada. OBJECTIVE: To determine the validity of acid-fast (AFB) smears of gastric a spirates (GA) in the diagnosis of pulmonary tuberculosis, and to assess the prevalence of nontuberculous mycobacteria (NTM) in GA isolates from such p atients. DESIGN: A retrospective case review of our experience with AFB smears (Kiny oun) and cultures of GA and sputum over a 3-year period. RESULTS: From 1994 to 1996 inclusive, 1155 GA were performed in 889 patient s. Mycobacteria were cultured from 109 (9%) GA. Thirteen of these were posi tive on smear (sensitivity 19%). All GA that were positive on smear were cu lture positive for Mycobacterium tuberculosis. There were no false positive smears (specificity 100%). The sensitivity and specificity of the sputum s mear mere 45% and 99%, respectively. Of the 96 culture positive, smear nega tive GA, 54 grew M. tuberculosis and 42 grew an NTM. Of 13 patients who had sputum and GA studied coincidentally, and in whom the sputum was both smea r and culture positive, the GA culture was positive in 13 and the smear was positive in eight (66%). CONCLUSION: AFB smear of GA is a relatively insensitive but highly specific indicator of pulmonary tuberculosis warranting institution of antitubercul osis treatment. Gastric AFB smear positivity appears to reflect a high baci llary burden within the respiratory tract.