treblechar
Forum Senior
Topics: 7
Posts: 101
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from Mass.gov The ability of persons who have TB infection to react to PPD may gradually wane. For example, if tested with PPD, adults who were infected during their childhood may have a negative reaction. However, the PPD could boost the hypersensitivity, and the size of the reaction could be larger on a subsequent test. This boosted reaction may be misinterpreted as a PPD test conversion from a newly acquired infection. Misinterpretation of a boosted reaction as a new infection could result in unnecessary investigations of laboratory and patient records in an attempt to identify the source case and in unnecessary prescription of preventive therapy for HCW's. Although boosting can occur among persons in any age group, the likelihood of the reaction increases with the age of the person being tested
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| doyoudig
Forum Guru
Topics: 144
Posts: 613
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Imagine a Person got infected with TB, but was never treated for his/her Latent TB. Now as the years pass by his immunity weans and now he/she gets another PPD Test and it comes out negative, b/c of the waning Immunity. (But even though this PPD Test was negative it caused a hypersensitivity rxn in his immunity-- This will cause a Booster Rxn on his/her next PPD testing)
Now the Guy/Gal gets yet another PPD test a year later (assume that the Gal/Guy had no contact to any Pt with active TB between these Test), and this time it comes out Positive -- This is called Booster rxn, which is often falsely read as an newly aqired TB Infection (even though in this case it is actually the result his/her old TB infection, that was left untreated)
To avoid this problem, 2 step PPD testing should be used as the Initial Test when repeat testing is anticipated (exp. Hospital workers, or nursing home residents or Pt w/ latent TB)
To perform a 2 step testing, a 2nd PPD test is done 1-3 weeks after the Initial Skin Test
--> If the 2nd Test remains negative then the Pt is assumed to be negative for Latent TB and any tests that are done after and that are + are the result of new infection
--> If the 2nd Test on the other hand is +, this is a Boosted response from a Prior TB Infection and the Pt should be treated for latent TB (not new infection)
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| fox
Forum Guru
Topics: 70
Posts: 727
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perfect...thank you
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