Comparison of a whole-blood interferon-gamma assay and tuberculin skin testing in patients with active tuberculosis and individuals at high or low risk of Mycobacterium tuberculosis infection.
BACKGROUND
QuantiFeron-TB (QIFN) is a whole-blood interferon-;gamma assay for the recognition of cell-mediated immune response to Mycobacterium tuberculosis infection.


OBJECTIVE
To compare the QIFN assay with the tuberculin skin test (TST) in patients with newly diagnosed culture-proven tuberculosis (TB) and healthy volunteers with high or low risk of latent M tuberculosis infection and to identify factors associated with discordance between tests.


METHODS
Two-hundred fifty-eight subjects underwent both assays. All participants completed a detailed questionnaire, and data from TB patients' medical records were collected.


RESULTS
In the entire study population, agreement between tests was moderate and the correlation between the magnitude of QIFN response and the TST induration diameter was significant. In volunteers with no known risk of exposure to M tuberculosis, the specificity of the assays was comparable. However, in subjects with active TB or those vaccinated with bacille Calmette-Guérin, the QIFN assay detected more reactors than did the TST. In these individuals, agreement between assays was poor and no correlation or only a weak correlation was found between the diameter of TST induration and the magnitude of the interferon-gamma responses.


CONCLUSIONS
The sensitivity of the QIFN assay is greater than that of the TST in patients with active TB before the initiation of anti-TB chemotherapy, but its specificity is influenced more by bacille Calmette-Guérin vaccination. The QIFN assay may provide an improvement over the current practice of the use of the TST to support diagnosis of active M tuberculosis infection in the clinic; however, QIFN cannot be considered an adequate replacement for the TST in the screening for latent infection.
Fietta
Anna
A
Department of Haematological, Pneumological, and Cardiovascular Sciences, Clinic of Resperatory Diseases, University of Pavia, Pavia, Italy.
Meloni
Federica
F
Cascina
Alessandro
A
Morosini
Monica
M
Marena
Carlo
C
Troupioti
Panaiota
P
Mangiarotti
Patrizia
P
Casali
Lucio
L
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002353:Carrier State; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007371:Interferon-gamma / Q000097:blood*; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009164:Mycobacterium Infections / Q000097:blood / Q000175:diagnosis; D009169:Mycobacterium tuberculosis / Q000302:isolation & purification*; D011336:Probability; D012016:Reference Values; D018570:Risk Assessment; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D014374:Tuberculin Test; D014397:Tuberculosis, Pulmonary / Q000097:blood / Q000175:diagnosis*
D007371:Interferon-gamma