Clinical utility of a T cell-based assay in the diagnosis of extrapulmonary tuberculosis.
OBJECTIVE
The aim of this study was to evaluate the QuantiFERON TB-2G (QFT-2G) results in patients with active extrapulmonary tuberculosis (E-TB) to determine whether QFT-2G test might be a reliable diagnostic method for detecting active E-TB infection compared with the tuberculin skin test (TST).


METHODS
TST and QFT-2G tests were performed for 35 patients with confirmed E-TB, 30 with probable E-TB and 45 who did not have E-TB.


RESULTS
For patients with confirmed E-TB, the positive rate of the TST was 57% and that of the QFT-2G test was 86%. For patients with probable E-TB, the positive rate of the TST was 60%, whereas that of the QFT-2G test was 80%. However, the positive rate of the TST was 51% and that of QFT-2G test was 9% for patients that did not have E-TB. The QFT-2G test showed a significantly lower percentage of false-negative results compared with the TST. The sensitivity and specificity of the TST for the diagnosis of active E-TB were 57% and 49%, respectively. By comparison, the sensitivity and specificity of the QFT-2G test were 86% and 84%, respectively. When the results of the TST and QFT-2G tests were separated by the site of E-TB, the positive rates for both tests in patients with miliary tuberculosis were lower than those in patients with other E-TB disease, although the difference was not significant.


CONCLUSIONS
The QFT-2G appears to be a reliable diagnostic test and in the appropriate clinical context QFT-2G may be more useful than the TST to support a diagnosis of E-TB. Studies are needed to evaluate its value also in situations of low clinical probability.
Kobashi
Yoshihiro
Y
Division of Respiratory Diseases, Department of Medicine, Kawasaki Medical School, Matsushima, Kurashiki, Japan. yoshihiro@med.kawasaki-m.ac.jp
Mouri
Keiji
K
Yagi
Shinichi
S
Obase
Yasushi
Y
Miyashita
Naoyuki
N
Oka
Mikio
M
D000368:Aged; D000942:Antigens, Bacterial / Q000097:blood*; D001426:Bacterial Proteins / Q000097:blood*; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D005260:Female; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013601:T-Lymphocytes / Q000378:metabolism*; D014374:Tuberculin Test / Q000379:methods; D014376:Tuberculosis / Q000097:blood* / Q000175:diagnosis*
D000942:Antigens, Bacterial; D001426:Bacterial Proteins; C117940:CFP-10 protein, Mycobacterium tuberculosis; C093276:ESAT-6 protein, Mycobacterium tuberculosis; D007371:Interferon-gamma