The QTF was not
completed in all children owing to inadequate blood volumes.
Finally, although the QTF used in this study is still in use, a
newer in-tube version which includes TB 7.7 as an additional
antigen is currently being marketed and differences between
responses measured by different generations of QTF test may be
considerable.34 An important potential distinction which we
have retained by using the QTF in the present study is the
ability to distinguish between different antigen responses; this
has been lost using the newer generation in-tube QTF which
combines all three antigens.