Evaluation of cut-off values of interferon-gamma-based assays in the diagnosis of M. tuberculosis infection.
METHODS
A chest disease centre in Istanbul, Turkey.


OBJECTIVE
The diagnostic accuracy of interferon-gamma-based assays for Mycobacterium tuberculosis infection may be improved by using lower cut-off values for the tuberculin skin testing (TST), QuantiFERON-TB Gold (QFT) and T-SPOT.TB (T-SPOT) assays.


METHODS
Three assays, TST, QFT and T-SPOT, were evaluated for their diagnostic performance with respect to different cut-off values. This evaluation was carried out in a comparative study involving 100 patients with untreated culture-confirmed cavitary pulmonary tuberculosis (TB) and 47 healthy subjects.


RESULTS
The sensitivities of the assays were: TST 70%, QFT 78% and T-SPOT 83.5%, while their specificities were TST 35%, QFT 89.4% and T-SPOT 84.8%. Both QFT and T-SPOT were significantly more specific than TST (both P < 0.001), but were similiar to each other (P = 0.5). Receiver operating characteristic analysis revealed that a cut-off value of 0.818 IU/ml for QFT maximises specificity without significant loss of test sensitivity. Using lower cut-off values for T-SPOT and TST, however, also increased the sensitivity of the assay but resulted in a significant decrease in specificity.


CONCLUSIONS
Lower cut-off values for TST, QFT and T-SPOT increased the sensitivity of each assay, but only with a lower cut-off value for QFT could specificity be maintained.
Soysal
A
A
Marmara University School of Medicine, Department of Paediatric Infectious Diseases, Istanbul, Turkey.
Torun
T
T
Efe
S
S
Gencer
H
H
Tahaoglu
K
K
Bakir
M
M
D000328:Adult; D000942:Antigens, Bacterial / Q000276:immunology*; D002478:Cells, Cultured; D005260:Female; D006801:Humans; D007371:Interferon-gamma / Q000097:blood*; D008297:Male; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000276:immunology*; D011237:Predictive Value of Tests; D012372:ROC Curve; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014373:Tuberculin / Q000276:immunology*; D014374:Tuberculin Test; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis* / Q000382:microbiology
D000942:Antigens, Bacterial; D014373:Tuberculin; D007371:Interferon-gamma