Hi Dr. My daughter who just turned 4yrs on April 1st, 2012 , had a negative ppd test in September 201 and now, at her 4 yr checkup on April 4th 2012 her Dr. decided to give her an entire physical again with another ppd, and it came back positive. My daughter is very healthy, never sick, but she & I were traveling on the NYC subway 2x s a day from Sept 11 - Jan 12 for a school program which is most likely how the pediatrician feels she was exposed. I took her on Friday the 6th for a chest x-ray which was negative for TB. I had another ppd on Sat, mine came back negative. Her test measured 13mm & the dr said the cut off is 15mm. She is strongly recommending INH for the 9 month duration for LBTI. The dr says bcs of her age & testing negative in Sept, she wants to do the INH. She is supposed to start the medication today but my gut feeling is saying no. Is it possible to re-test her or is there another test to do & is it possible to have a false +? Do you have any recommendations?