following a tuberculan test, how long does the testing agent remain in the body?

Answer 1

There is so much misinfomration here that I feel the need to set things straight.

First off, TB skin tests have to be read after 48-72 hours- the 30 min test is an allergist's skin test, not the tuberculosis test.

Next, While its true that if you are skin tested often enough, you can turn skin test "positive" after being "negative" (this is what the first respondent meant by a "failed scratch test"). BUT- that is NOT due to the persistence of the agent in the body but the persistence of the immune response to the agent. Tuberculin, the name of the reagent that is injected, is degraded within a few hours to days inside of tissue macrophages, but the immune response to the antigens may remain for a few months.

Obviously , Anne is mightily confused about what a tuberculin test is- it has nothing to do with antibiotics or allergy testing- it is the injection of purified proteins from the tuberculosis germ itself, and it is used to measure immune exposure, not allergy.

Immune responses to tuberculosis antigens are well studied and well characterized. If you have tuberculous DISEASE you will likely have lifelong positive tests to skin testing. If you are TB EXPOSED BUT DONT DEVELOP DISEASE you will also likely remain skin test postive for life. If you are VACCINATED against TB with the BCG vaccine your skin test will likely be very weakly positive for a few months to a year, but not usually strong enough to generate a positive skin test two years later. If you are repeatedly skin tested over a period of months, there is a low chance you will eventually test postive, but it wil prpbably take several skin tests before this happens, if it happens at all, and the skin test positivity will wane early, even earlier than after BCG vaccination.

Answer 2

It can stay in the body for months, long enough for you to fail a subsequent "Scratch" TB test. If this happens you will need to have a Chest X-Ray to establish that you don't have TB. This is a common problem with immigrants to the US.

Answer 3

tuberculin testing or skin testing as far as i know is a form of LOCALIZED injection of a certain medication (mostly antibiotics) to rule out allergy to certain drugs... once the skin testing is done, the results can be read after 30 minutes and after which it disappears... although not in all cases...

Answer 4

About a week