Usefulness of gastric aspirate for the diagnosis of smear-negative pulmonary tuberculosis

Introduction: Gastric aspirate can be useful for the diagnosis of pulmonary tuberculosis (TB) in patients with smear-negative pulmonary TB or without sputum production. The gastric aspirate smear technique has low sensitivity, and a previous report demonstrated that no patient was diagnosed by only gastric aspirate analysis. However, some patients with TB have been negative on sputum examination but positive on gastric aspirate examination, and the incidence of such cases is uncertain. Therefore, this study investigated the usefulness of gastric aspirate in the diagnosis of pulmonary TB.

Methods: To analyze the diagnostic accuracy of gastric aspirate examination, the data of 513 patients with negative sputum smears or a lack of sputum production, including 203 patients with pulmonary TB (39.6%) and 93 patients with nontuberculous mycobacteriosis who underwent gastric aspiration at Fukujuji Hospital from January 2016 to March 2021, were collected retrospectively.

Results: The accuracy rates of gastric aspirate examination for the diagnosis of pulmonary TB were as follows: 21.2% sensitivity and 91.9% specificity for smear positivity, 55.8% sensitivity and 99.6% specificity for nucleic acid amplification test positivity, and 71.4% sensitivity and 100% specificity for culture positivity. Twenty-three patients (11.2%) were diagnosed by gastric aspirate examination alone. Among the 356 patients who underwent three repeated sputum examinations in addition to gastric aspirate examination, the cumulative diagnostic rate for the 3 mycobacterial examinations plus gastric aspirate examination was higher than that for only three sputum examinations.

Conclusions: Gastric aspirate is useful for the diagnosis of TB in patients with smear-negative pulmonary TB or without sputum production.