Purpose: To evaluate the diagnostic utility and predictors for determinate results of an enzyme-linked immunospot assay using induced sputum cells (IS ELISPOT) for a rapid diagnosis of pulmonary tuberculosis (TB).
Materials and methods: Subjects suspected of pulmonary TB who had either sputum acid fast bacilli smear-negative or not producing sputum spontaneously were prospectively enrolled. ELISPOT assay was performed using cells from induced sputum.
Results: A total of 43 subjects, including 25 with TB (TB group) and 18 with non-TB disease (non-TB group) were enrolled. Results of IS ELISPOT were determinate in only 17/43 (39%) subjects, but all of determinate results were consistent with the final diagnosis. Of the 43 sputum samples, 11 (26%) were inadequate to perform IS ELISPOT. Of 32 adequate sputum samples, the proportion of determinate results was significantly higher in the TB group (75%, 15/20) than in the non-TB group (17%, 2/12) (p=0.002). The status of active TB was a unique predictor but smear positivity was not a significant predictor for determinate results. In addition, sensitivity of IS ELISPOT (75%, 9/12) in smear negative TB was higher than that of TB-polymerase chain reaction (25%, 3/12).
Conclusion: IS ELISPOT showed relatively high diagnostic value and accuracy in the TB group, independent of smear positivity. IS ELISPOT may provide additional diagnostic yield for microbiological tools in the rapid diagnosis of smear-negative TB.
Keywords: Tuberculosis; enzyme-linked immunospot assays; immunodiagnosis; induced sputum.