In addition to categorical representation of IGRAs based on
manufacturers’ guidelines, individual and total antigen
responses for T-SPOT.TB (ESAT-6 and CFP-10, spot count per
250 000 peripheral blood mononuclear cells) and IFNc QTF
antigen response (IU/ml) were described as continuous measures.
19 Comparisons between children and adults were performed
using the Pearson x2 and Wilcoxon rank sum tests for
dichotomous and continuous tests results, respectively. Receiver
operating characteristic (ROC) curves were generated to
compare individual continuous IGRA antigen responses in
relation to the M tuberculosis contact score, which was used as
a surrogate gold standard. Correlations were explored between
T-SPOT.TB and QTF for the ESAT-6 and CFP-10 assay levels for
children and adults using the Spearman rank correlation
coefficient. The T-SPOT.TB spot count and QTF IFNc IU/ml
were both transformed to the natural log scale for graphical
purposes. Missing data and indeterminate results were excluded
from analyses.