Discrepancy Between the Tuberculin Skin Test and the Whole-Blood Interferon γ Assay for the Diagnosis of Latent Tuberculosis Infection in an Intermediate Tuberculosis-Burden Country

Evaluation of the diagnostic utility of a whole-blood interferon-γ assay for determining the risk of exposure to Mycobacterium tuberculosis in Bacille Calmette-Guerin (BCG)-vaccinated individuals

“…It has been previously reported that in vitro whole blood IFN-γ response to PPD correlates well with TST (Black et al, 2001). We found poor agreement between QuantiFERON® and PPD tests in all groups, which is consistent with other reports (Brock et al, 2001(Brock et al, & 2004Mori et al, 2004;Kang et al, 2005) and confirms that QuantiFERON® test is substantially more specific than TST in BCG vaccinated persons. Brock and co-workers (2004) showed that, in BCG-vaccinated persons, 50 % of high-exposure and 6 % of lowexposure group responded to QuantiFERON®, which gives the similar overall prevalence to those of the unvaccinated subjects, 53 % and 5 %, respectively.…”

“…Brock and co-workers (2004) showed that, in BCG-vaccinated persons, 50 % of high-exposure and 6 % of lowexposure group responded to QuantiFERON®, which gives the similar overall prevalence to those of the unvaccinated subjects, 53 % and 5 %, respectively. A more recent study by Kang et al (2005) was performed in Korea and showed 4 %, 44 % and 81 % of positive responses to QuantiFERON® test in low risk, high risk subjects and TB patients, respectively whereas ours are 10.4 %, 52 %, and 79.2 %. The sensitivity of the assay in TB patients was similar in both studies.…”

“…Another plausible explanation for this observation is the difference in regional prevalence rates because the medical students were recruited from different regions in the two studies. In the high risk group, we also obtained a higher response rate than that of Kang et al (2005). This may be because of the different characteristics of the cohort in our study.…”

“…The subjects comprising the low risk group were medical students in both studies. Kang et al (2005) mentioned that the 4 % of IFN-γ response in low risk individuals was underestimated probably because the IFN-γ assay reflects recent rather than remote TB infection. In our study, however, we obtained 10.4 % of positive rate which is twice higher but this is still low considering the predicted prevalence of TB infection (33 %) in the Korean population (Korean National Tuberculosis Association, 2005).…”

“…Several studies have reported that RD1-based (ESAT-6 and/or CFP-10) IFN-γ assays have higher specificity than TST, and are less influenced by previous BCG vaccination (Ravn et al, 1999;Arend et al, 2000;Brock et al, 2001;Mori et al, 2004;Pai et ai., 2004). Newer generation test kits using these two individual antigens have already been developed and reports of their utility are now beginning to emerge (Pai et ai., 2004;Ferrara et al, 2005;Kang et al, 2005). More recently, an enhanced and simplified QuantiFERON® assay has been developed using a mixture of overlapping peptides representing ESAT-6, CFP-10, and a portion of the TB antigen TB7.7 in order to enhance the sensitivity of the assay.…”