But please keep in mind, that most doctors' eyes would glaze over and
turn off if you requested this cutting edge testing.

I am not trying to discount his data, but doctors in this country are resistant,
poorly informed and also form value judgements against the patient, in the form of mean diagnoses in the chart... hypochondriac, malingerer etc and that goes
on YOUR record for other doctors and insurance to read.

So while we need good testing... I don't think it is available to most people reading here in US (and perhaps in other countries).

Here in the US it is just becoming more common to do MMA instead of B12 serum levels. MMA is a precise tool to show if B12 is working at all, since the test measures the only precise effect of B12 on one enzyme system. You could have
tons of free B12 floating around in the blood doing NOTHING... for all anyone knows.

Also binding proteins are dependent on protein intake, and a whole slew of other enzyme functions having to do with blood proteins, before it can be carried around. Aging and other variables can really negatively affect these proteins.

The subject is just huge...many things working or not working in concert properly. Medicine is just not equipped for this yet.