Whole blood interferon-γ release assay is insufficient for the diagnosis of sputum smear negative pulmonary tuberculosis.
OBJECTIVE
We investigated the value of an interferon-γ release assay (IGRA) for the diagnosis of active pulmonary tuberculosis (PTB) among sputum smear negative PTB suspects in an environment with intermediate burden of PTB and high Bacillus Calmette-Guerin (BCG) vaccination rate.


METHODS
We retrospectively reviewed IGRA, medical records, chest PA and CT scan of PTB suspects seen at Gangnam Severance Hospital, Seoul, Korea from Oct. 2007 to Apr. 2013. "Active PTB" was diagnosed when 1) M. tuberculosis culture positive, 2) confirmation by pathologic examination; or 3) clinical findings compatible with TB.


RESULTS
Of 224 sputum smear negative PTB suspects, 94 were confirmed as having active PTB. There were no statistically significant differences in the diagnostic yield of IGRA between immunocompromised and immunocompetent sputum smear negative PTB suspects. IGRA did show superior sensitivity [81.9%, 95% confidence interval (CI); 74.13-89.70%] in the diagnosis of sputum smear negative PTB when compared with chest high-resolution computed tomography (HRCT), tuberculin skin test (TST), and chest X-ray (p<0.001). Also, IGRA showed highest negative predictive value (82.7%, 95% CI; 75.16-90.15%) when compared with HRCT, TST and chest X-ray (p=0.023). However, combining the results of IGRA with those of HRCT, TST, or both did not increase any diagnostic parameters.


CONCLUSIONS
Failure to increase diagnostic yields by combination with other diagnostic modalities suggests that additional enforcement with IGRA may be insufficient to exclude other diagnoses in sputum smear negative PTB suspects and to screen active PTB in an environment with intermediate TB prevalence and a high BCG vaccination rate.
Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Korea.
HeeJin
H
Park
Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Korea.
Jung Ar
JA
Shin
Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Korea.
Hyung Jung
HJ
Kim
Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Korea.
Chul Min
CM
Ahn
Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Korea.
Yoon Soo
YS
Chang
D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D059425:Interferon-gamma Release Tests / Q000379:methods*; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D013183:Sputum / Q000382:microbiology*; D014397:Tuberculosis, Pulmonary / Q000097:blood / Q000175:diagnosis* / Q000378:metabolism
Sputum smear negative pulmonary tuberculosis; active pulmonary tuberculosis; interferon-gamma release assay