matter of fact, if you have a positive ppd once , you are almost certain to be positive for your lifetime . thats why when you know you are positive you should never have the test again because someitmes you can have bad skin reaction from the test itself. If i were you i would save that paper that says u were ppd positive and that u went thru 9 months of inh in a 'safebox' so that next time someone wants to test you for tb u can show that and you will get away just with a chest xray.