Methylation issues are checked via specialized blood tests -- see
https://www.healingwell.com/community/default.aspx?f=30&m=2004679
There is a test for XMRV, but most LLMD's right now are saying there is little point testing for it because they don't know the best treatments yet for it.
IMHO, IV Vitamin C would be helpful for XMRV (and any other viruses) because Vitamin C is toxic to viruses and kills them. There are other things that can help with viruses as well, such as certain herbs (elderberry, golden seal, Pau d' Arco, Olive Leaf, etc.) and some theraputic grade Essential Oils (peppermint, lemongrass, lemon, etc.).
KPU = HPU (urine test) See http://betterhealthguy.com/joomla/images/stories/PDF/kpu_klinghardt_explore_18-6.pdf for more info on this.