Sputum culture for the diagnosis of tuberculous pleural effusion: analysis of absolute and incremental yields.

Introduction: Pleural fluid culture yield in tuberculous pleural effusion (TPE) is disappointing in immunocompetent hosts. Herein, we attempt to define the role of serial sputum cultures in the diagnosis of TPE.
Material and Methods: We identified cases diagnosed with TPE over a16-year period in ahigh-prevalence US hospital. Absolute yields of one, two, and three sputa were calculated as well as the incremental yield of adding second and third sputa. These calculations were then performed separately for expectorated and induced sputum and for patients with and without infiltrates on chest X-ray.
Results: Sixty sputum collections were performed in 46 patients with TPE. The per-patient sensitivity of sputum culture was 45.6%. On aper-sputum collection basis, the overall yield of the first sputum was 30%, of two sputa 39%, and of three sputa 54%. The corresponding incremental yields were 9% and 15%, respectively. The three-sputum yields of expectorated and induced collections were similar. The three-sputum yield in patients with infiltrates on X-ray was 11% lower than that in those without infiltrates.
Conclusions: Serial sputum collection of three specimens can be expected to produce ayield of > 50% in cases of suspected TPE regardless of whether obtained by expectoration or induction, and the yield increases incrementally.