Within-Subject Variability and Boosting of T-Cell IFN-γ Responses Following Tuberculin Skin Testing.

Comparison of same day versus delayed enumeration of TB-specific T cell responses

“…6 This evidence-based definition is more robust compared to the conventional definition (IGRA conversion Z change from a negative to positive result relative to the cut-point and reversion Z change from a positive to negative result relative to the cut-point). 7 Using the evidence-based definition, although there were 9 conversions/reversions (Fig.…”

“…(i) Based on data from van Zyl-Smit and colleagues, 6 conversions were defined as an increase in interferon gamma (IFN-g) response from below 6 spots to above 9 spots (greater than or equal to 3 spots on either side of the manufacturer's cut-point of 24 SFCs/million PBMCs), and reversions were defined as a decrease in IFN-gamma response from above 9 spots to below 6 spots. (ii) The conventional method, as used by the manufacturer, defines an IGRA conversion as a change from a negative to positive result relative to the cut-point, and a reversion as a change from a positive to negative result relative to the cut-point.…”

“…However, 3 of the 9 conversions/reversions fall within the 'borderline zone'. 6 Hence, only 6 (4 conversions and 2 reversions) were considered to be true conversions/reversions (B). The medians are indicated as horizontal solid lines and the cut-point (24 SFCs/million PBMCs) is indicated as a horizontal dotted line.…”

“…For the whole group, 2 conversions and 1 reversion occurred. None of the conversions/reversions fall within the 'borderline zone'6 and were thus all considered to be true conversions/reversions (B). The medians are indicated as horizontal solid lines and the cut-point (24 SFCs/million PBMCs) is indicated as a horizontal dotted line.The difference between the number of conversions/ reversions for group 1 (day 0 without T-Cell Xtend and day 1 without T-Cell Xtend ) vs. group 2 (day 0 without T-Cell Xtend vs. day 1 with T-Cell Xtend ) was not statistically significant (Wilcoxon Signed Ranks test 2-tailed p-value Z 0.809).…”

Commercial Interferon Gamma Release Assays Compared to the Tuberculin Skin Test for Diagnosis of Latent Mycobacterium tuberculosis Infection in Childhood Contacts in the Gambia

“…Delayed presentation by TB cases (mean 9 weeks) in the presence of early reversion of IGRAs may contribute. [22][23][24] Also, a third of TB cases in The Gambia are infected with M. africanum which exhibits an attenuated response to ESAT-6 in both cases and their contacts. 25 Surprisingly higher specificity of TST compared with IGRAs to the exposure gradient is difficult to explain, but the higher specificity of TST when compared with the IFN-␥ ELIS-POT response to the same PPD antigens, 11 suggests that the type of immune response elicited is at least partially responsible.…”