Presence of alveolar macrophages as a criterion for determining the suitability of sputum specimens for bacterial culture.

The microscopic and bacteriological findings in paired saliva and sputum specimens from 66 patients with chronic bronchitis were compared in order to determine whether the presence of alveolar macrophages is a valid criterion for determining the suitability of a sputum specimen for bacterial culture. Alveolar macrophages were mainly present in sputum specimens, the culture results of which differed from the culture results of the matching saliva specimen (p less than 0.001). Sputum specimens containing alveolar macrophages appeared to be contaminated less with oropharyngeal flora than specimens which did not contain alveolar macrophages. Potential pathogens such as Streptococcus pneumoniae and Haemophilus influenzae were isolated only from sputum specimens containing alveolar macrophages. It is concluded that the presence of alveolar macrophages indicates that sputum originates from the lower respiratory tract. The results also showed that the presence of leukocytes in sputum may be considered significant if alveolar macrophages are also present.