Hi Lynn, I think it was 10/10 I had a positive jcv test. Then 1 yr later my test was negative.

I have had a couple test at the 6 mth interval done at Quest-negative and close to the correct month for the stratify year test in 2012 - NEGATIVE!! I have been on Tysabri for 6 1/2 years
So yes, it can happen

Linda