PPD Question

Is it possible to test positive for PPD at one time and without treatment have a negative test years later.  In 1992, I had a reported PPD positive test at the same time I was having fever of unknown origin and pneumonitis in left lingula.  I also remember their being a positive reaction years before when I was a teenager.  My mother has always tested positive since a child but has never required treatment.  Recently, I had a PPD and it was clearly negative.  So, would the this mean the other tests were false positives or could my immune system have changed.  Lastly, what explanation could there be for this?

[National Jewish]

Yes it is possible to test positive for PPD at one time and without treatment have a negative test years later.  Here are 2 other explanations.
1) Your immune system could be waning as you age.  If a "booster" PPD test were done, you might be positive.
2) Also, many people may have weakly positive PPD skin tests if they have been exposed to or come from areas in the country where there is a high concentration of environmental mycobacteria, such as the southeast.