Routine hospital use of a new commercial whole blood interferon-gamma assay for the diagnosis of tuberculosis infection.
BACKGROUND
Interferon (IFN)-gamma blood tests may improve the current level of diagnostic accuracy for tuberculosis infection. The QuantiFERON-TB Gold (QFT-Gold) has been used in selected populations and shows higher specificity than the tuberculin skin test (TST).


OBJECTIVE
To evaluate the QFT-Gold test in unselected patients and assess the level of agreement with the TST.


METHODS
The test has been routinely performed on whole blood samples in our microbiology laboratory for 8 months. Demographic, clinical, and microbiological data have been collected and correlated to the QFT-Gold results.


RESULTS
Of 318 patients tested, 68 (21.4%) gave an indeterminate (low positive mitogen control) QFT-Gold result. Indeterminate results were significantly overrepresented in patients with a negative TST (28.9% vs. 6.6% in TST-positive patients; p < 0.0001, chi2 test) and were more frequent in patients receiving immunosuppressive therapies than in those who were not receiving such treatments (odds ratio, 3.35; 95% confidence interval, 1.84-6.08; p < 0.0001). After excluding indeterminate results, the concordance between QFT-Gold and TST was significantly lower in Bacille Calmette-Guérin-vaccinated individuals (41.5%) than in nonvaccinated individuals (80.3%) (p < 0.0001). In 11 patients with active tuberculosis (5 culture-confirmed), QFT-Gold provided more positive results than the TST (66.7% vs. 33.3%; p = 0.165).


CONCLUSIONS
The QFT-Gold test is feasible in routine hospital use for the diagnosis of tuberculosis infection. As with the TST, immunosuppression may negatively affect the test's performance, with a significant rate of indeterminate results in the most vulnerable population.
Ferrara
Giovanni
G
Section of Respiratory Disease, Department of Oncology, Haematology and Respiratory Disease, University of Modena and Reggio Emilia, Modena, Italy.
Losi
Monica
M
Meacci
Marisa
M
Meccugni
Barbara
B
Piro
Roberto
R
Roversi
Pietro
P
Bergamini
Barbara Maria
BM
D'Amico
Roberto
R
Marchegiano
Patrizia
P
Rumpianesi
Fabio
F
Fabbri
Leonardo M
LM
Richeldi
Luca
L
D000328:Adult; D000368:Aged; D003955:Diagnostic Tests, Routine / Q000379:methods*; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods; D007371:Interferon-gamma / Q000097:blood*; D008297:Male; D008875:Middle Aged; D012882:Skin Tests; D014376:Tuberculosis / Q000175:diagnosis*
D007371:Interferon-gamma