What should I be tracking to make sure I don't get the JC virus?

Here is My Question:
I'm new to MS. JCV Antibody positive. I start Tecfidera today. I need to know what I should be measuring/tracking to ensure I don't get the JCV Virus. My lymphocyte count is 1.2 which doesn't translate to the absolute 400,500 etc. numbers I keep reading about. 

Can you please list the various blood tests I should be testing for and what levels of each are good or bad?

Answer:
Welcome to the site. If you search for JC virus and Tecfidera using the search button on the home page, you will find a lot of information already posted on this issue.

At the present time you can forget about the JC virus antibody index while you are on Tecfidera. No one has demonstrated an association between this lab test and risk of PML in Tecfidera treated patients. Focus instead on your absolute lymphocyte count. Your count of 1.2 translates to 1,200 absolute lymphocytes (multiple the lab result by 1000). This is a very good number. A normal count is anything over 900-1000 or 0.9 to 1.0 on the lab test. We become concerned when the value drops below 600 or 0.6 on the lab test. If your lymphocyte count drops below 800 or 0.8 while taking Tecfidera, we usually recommend more frequent testing (every 3 months). If it drops below 600 or 0.6, we test it every month and consider stopping Tecfidera, at least temporarily, if this reduction persists more than 2 months. Of course, whether it is wise to stop Tecfidera depends on your individual circumstances and risk factors. The best decision can only be reached after a thorough discussion with your MS specialist.

A low absolute lymphocyte count is generally associated with a higher risk of rare atypical infections and malignancies. For instance, people infected with the HIV virus develop very low lymphocyte counts without treatment, and this is the reason people with HIV experience unusual infections and malignancies without treatment.

Revere (Rip) Kinkel MD
Director of the Multiple Sclerosis Program
Professor of Clinical Neurosciences
University of California San Diego