You have to have regular blood tests to determine if you've developed the JC Virus Antibodies. If test is positive than you will be tested against Anti-JCV Antibody Index (Stratify JCV) that further defines the risk level of developing PML

I tested with a high positive before beginning Tsyabri so 2 years is my max
I did hesitate as the PML is a scary thing to think about
Tried 2 other drugs beforehand but one I had liver issues and the other wasn't working ( Avonex and Copaxone)
I was declining fast and had numerous new lesions so Neurologist was pretty much saying I needed the more powerful med
I get a brain MRI every 6 months to monitor the PML possibility
He doesn't bother with retesting for the JC virus with bloodwork as once your positive your positive
Good luck to you
I haven't had any side effects and no new lesions or activity since taking it
Felt better after the 4th infusion
Hoping the new drug
Ocrolizunab gets out in market soon as that's what I'll probably be switching to in December 2017 and I'm pretty sure it doesn't have the PML risk

I was on tysabri for 2 years. Every time I asked the doctor about JC he told me they measured by a number. Since he took me off after two years I assumed I was positive. I never had any problems while on tysabri.

Ok. Thanks. Good to know

When I spoke to my tysabri nurse, she says it can go either way.