A Perspective on Sputum Analyses in Pneumonia

Abstract

We reviewed the medical literature to assess the relative accuracy of lower respiratory tract secretion cultures obtained by expectoration (ES), by tracheal suction (TS), and by transtracheal aspiration (TTA). There are controversy and conflict concerning methods of sampling sputum. Routine ES is generally reliable in lower respiratory tract infections when the isolated organism could not be considered an oropharyngeal contaminant. In other instances, ES handled routinely is frequently inaccurate. By microscopically screening ES and processing only "good" specimens, one may possibly minimize the inaccuracy of routine ES cultures. By using special techniques, one can improve the accuracy of ES; however, false-positive information is still frequently generated. ES must be swarming with a morphologically distinct organism for gram smears to be predictive of subsequent cultures. These same comments apply to TS analyses. TTA appears to diminish the deficiencies of ES and TS analyses. But although it generates less false-positive and false-negative information, TTA still has these shortcomings and should not be used as a standard for comparing other methods. From a laboratory standpoint, TTA is more accurate than TS and ES. However, the important issue is whether the outcome in pneumonia depends on any sputum analysis. In order for anyone to know when and in whom the cost of TTA, ES, and TS is worth the benefit, a prospective study of these methods must be undertaken in all patients with pneumonia. Until this study is done, the role of TTA, ES, and TS in evaluation of lower respiratory tract infections will remain controversial.