Table 2 Characteristics and results of studies on within-subject variability of the IFN-γ response
Study (Year of publication) | Country | IGRA(s) used | Subjects (total number of tests) | Visits (Days) | Summary of results |
|---|---|---|---|---|---|
Studies in countries with a high incidence of TB (≥ 100 per 100,000 population and year)* | |||||
Veerapathran et al. (2008) [21] | India | QFT | 14 (56) | 0, 3, 9, 12 | Over a two-week period, two out of 14 subjects (14%) had a QFT reversion. Overall, reproducibility of the quantitative results was moderate. A non-significant 30% reduction in mean IFN-y response was observed between visits. An increase of up to 16% in IFN-γ concentration was within the expected within-subject variability. |
Van Zyl-Smit et al. (2009) [20] | South Africa | QFT T-SPOT | 26# (88) | 0, 7, 14, 21 | Over a three-week period seven out of 26 volunteers had a conversion or a reversion (1x QFT, 6x T-SPOT). A change in mean IFN-γ response of ± 80% (QFT) or ± 3 SFCs accounted for 95% of the within-subject variability. |
Detjen et al. (2009) [43] | South Africa | QFT | 27 (54) | 0, 3 | Over a three-day period no qualitative changes in the QFT results were noted in 15 subjects, but a partly substantial within-subject variability in IFN-γ response was observed (intra-class correlation = 0.80). |
Studies in countries with a low incidence of TB (< 20 per 100,000 population and year) | |||||
Belknap et al. (2009)†[24] | USA | QFT T-SPOT | 117 (234) | 0, 7–21 | Over a three-week period seven out of 117 (6%) and eight out of 105 (8%) had a conversion or reversion with QFT or T-SPOT respectively. |
Ringshausen et al. (2011) [44] | Germany | QFT T-SPOT | 35 (158) | 0, 7, 14, 21, 28 | Changes of ± 70% (QFT) and ± 60% (T-SPOT) in mean IFN-γ response accounted for 95% of the within-subject variability. Inconsistent results were significantly more frequent with QFT (29%) than with T-SPOT (9%). |