Diagnosis of tuberculosis: routine cultures of bronchial washings are not indicated.

During a five-year period, cultures of bronchial washings for Mycobacterium tuberculosis were obtained almost routinely (859 of 1,012 bronchoscopic examinations.). This practice proved costly, and the diagnostic yield was extremely low. Only three cases were diagnosed solely by this method (0.35 percent). Five other cases were false-positive. Additionally, 39 patients with known active pulmonary tuberculosis had false-negative cultures of bronchial washings; 13 of these 39 patients were receiving antituberculosis drugs at the time of their bronchoscopic examinations. The inhibitory effect of local anesthetics upon the growth of M tuberculosis is the possible cause for the remaining 26 false-negative cultures. We conclude that bronchoscopic examination and culture of bronchial washings are not the best sources for diagnosis of pulmonary tuberculosis and that cultures of sputum and/or gastric washings are usually sufficient. The practice of obtaining routine cultures of bronchial washings in known pulmonary tuberculosis is of questionable value, when nearly two-thirds may be false-negative.