Intra-assay reliability and robustness of QuantiFERON(R)-TB Gold In-Tube test in Zambia.
BACKGROUND
Interferon-gamma (IFN-gamma) release assays (IGRAs), such as the QuantiFERON-TB Gold In-Tube test (QFT-GIT), are becoming a preferred method for diagnosis of tuberculosis (TB) infection in many industrialised countries. However, data on the effectiveness of IGRAs in high TB-HIV (human immunodeficiency virus) endemic and resource-limited settings, such as Zambia, are limited.


OBJECTIVE
To determine the intra-assay reliability and robustness of QFT-GIT in a field setting in Zambia.


METHODS
During July-October 2007, 109 adult smear-positive TB patients were recruited to determine QFT-GIT reliability and the effect of a 24-h delay in incubation. Two simulated laboratory experiments were also performed using 9-14 volunteers, to explore the effect of power outages during incubation and storage temperature of collection tubes on IFN-gamma responses.


RESULTS
QFT-GIT intra-assay concordance was 91.7% (kappa = 0.8). Discordance was observed for nine patients, of whom six were HIV-positive. There was evidence of an association between HIV status and discordant results (OR 1.98, 95%CI 1.06-3.67, P = 0.03). A 24-h delay in incubation changed results for 25 of the 109 (22.9%) patients. Power outages that altered incubation time reduced IFN-gamma responses.


CONCLUSIONS
Although QFT-GIT seems reliable in this setting, we have identified operational factors that affect its robustness. These factors may influence the effectiveness of this test in similar resource-limited settings.
Shanaube
K
K
Zambia AIDS-Related Tuberculosis (ZAMBART) Project, University of Zambia, Lusaka, Zambia. kshanaube@zambart.org.zm
De Haas
P
P
Schaap
A
A
Moyo
M
M
Kosloff
B
B
Devendra
A
A
Raby
E
E
Godfrey-Faussett
P
P
Ayles
H
H
D000328:Adult; D011211:Electric Power Supplies; D005260:Female; D015658:HIV Infections / Q000150:complications*; D006801:Humans; D007371:Interferon-gamma / Q000032:analysis*; D008297:Male; D015203:Reproducibility of Results; D013048:Specimen Handling / Q000379:methods; D013696:Temperature; D013997:Time Factors; D014376:Tuberculosis / Q000175:diagnosis*; D015024:Zambia
D007371:Interferon-gamma