I'm sure the ideal answer would be 'both', but that is unlikely to be possible. I'd also love input on these other ordered tests -- before or after starting B12? Homocysteine cystathionine (or CBS polymorphisms, but I'm guessing this is cheaper?) 2-methylcitrate GSH (Glutathione, in plasma) GSSG (oxidized Glutathione, test both) S-adenosymethionine (in RBC) S-adenosylhomocysteine (RBC, test both for ratio) And, hello everyone . I haven't been posting because I've been too brain-foggy, but have been reading a little.