Hello and thanks for the query
is said to be positive if redness
at the site if more than 5 mm unless it is infected. As you have described their is bump I think this could be infected. It is better to consult you treating doctor and get it confirmed. Your treating doctor can correlate it with clinical finding and get to a decision. Any delay in the treatment of TB can create problem. You can also go for TB Elisa
test as a confirmatory test for TB if you has some doubt.
Hope I have answered you query.