I have had the MMA test which was okay in my case. No, I would never suggest a CSF test, I was only saying that it was stated on one of the reference sites that it was the only "perfect" measurement. I have FMS as well. It seems like the more I read here, the less likely it seems that changing the doseage form is sensible. If one takes enough by mouth of a methyl form, it should work. Also, I have homocysteine levels done which have been fine and are allegedly an early sign of deficiency of B 12.
Thanks again for all those who took the time to respond.
Karen S.