What does a positive TB test look like?
I think your talking about the Mantoux test(skin test). They check you 48-72 hours after it is injected under your skin(normal the forearm). The size of the induration( or whelp as you may call it) shows whether or not you have been exposed to bacteria that causes TB. It does not however tell you if you have an active case or if it is dormant. Only a chest x-ray can do that. Here’s how to read it, A induration less that 5 mm is seen to be negative unless you are immune suppressed (like AIDS or other diseases), greater than 5mm is a good indication that you have been exposed to the bacteria. A chest x-ray and sputum culture would be next in line to see if you have an active case. They are looking for the acid-fast bacilli that cause TB.
A positive TB test is red & raised. This ‘induration’ varies from person to person, depending on exposure history, country of birth, and BCG history. Usually anything over 10 mm induration is considered positive, although 5 mm may also be considered positive in some circumstances, eg. immune suppressed persons or close contact with infectious TB.
