some light reading, page-69

OK Lopez I will respond the article you posted.
On the surface it looks like a good idea to use the In Tube nil sample tube as a source for the serology test which is then used to differentiat LTBI from active disease.
The one drawback is the clinicians impression of serology (antibody) tests. These tests have been aroud for a while and many clinicians think they have been foisted onto the poor, high TB burden countries even though many studies have shown them to have low sensitivity, specificity or both.
I could not see a sensitivity figure for the antibody test used in this study but I would be surprised if it is too good. Therefore clinicians would be reluctant to use a negative result to rule out active TB.
However, if the sensitivity and specificity of the antibody test are high (not likely in my opinion) then it would undoubtedly be useful.
Alex