Hi, Sparrow.
It sounds as though you might be one of the people whose cells are not able to convert folic acid to chemically reduced folates very well, and that you have developed a functional B12 deficiency. The combination of high RBC folic acid, high serum folate, low glutathione, high methylmalonic acid and high MCV and MCH suggests that.
If the methyl trap mechanism were operating alone, it's true that the serum folate would rise. However, in ME/CFS, the serum folates are observed to be low. Prof. Marty Pall has convinced me that this is due to peroxynitrite reacting with methylfolate and breaking it down. There is published evidence for this reaction.
RBCs obtain their folate during their initial production, and after that, they don't use it, but just act as storage reservoirs. When they are broken down (about 4 months later), they release their folate. The same is true of the B12 they contain.
Having a high RBC folic adid suggests that there was a lot of folic acid available at the time the RBCs were formed, but that it was probably not being chemically reduced at as high a rate as normal by the DHFR (dihydrofolate reductase) reactions.
Hopefully you will experience good results when you switch to methylfolate, which is a reduced form of folate and is the one directly needed by the methionine synthase reaction, which is inhibited by the functional B12 deficiency, which lowers the synthesis of methylfolate.
Best regards,
Rich