I don't understand your question.

When one is TESTING for B12 levels, then stopping the supplement is important. Testing is done to show you what you have at that moment. If you are taking vitamins and get vitamin testing done, the amount floating around in the serum will not be your "normal" amount...it is artificially elevated. The ranges for the vitamins were made using people NOT taking any supplement. They are to show a base line of statistic norm therefore.

The injections are 1000mcg right into the tissues. According to the table link I gave you 150mcg were then measured in the serum. 1000mcg of oral gave 13mcg in the serum.

The injections are typically given daily for a few days, then once a week then once a month. Oral is taken once a day on an empty stomach every day.

So stopping the injections for at least a week is a good idea if you want to see what your values are more accurately. If you use any supplement for any length of time, and not establish a base line of "before".... then you will create a new baseline which will be higher overall. (and higher even than that if you don't stop taking the supplement).

The purpose of testing is to see what you have before any intervention is done. That then would guide any treatment decisions and choices.

B12 is only ONE treatment choice for PNers. It will really only work if you were low to begin with. And if you are not tested before starting supplements of it, you will never know your starting value in the first place. If your PN is caused by another reason, that would have to be discovered too.

One latent sign of low B12 is an elevated MCV in the blood testing CBC panel. If this is very high normal, or out of the normal high range...it SUGGESTS there is not enough B12 to make normal cells. Anemia as a sign is often one of the last symptoms of low B12 status, with neurological signs appearing first. Dr. Snow's article on the B12 thread explains that in his paper.

So far metformin is not a high B12 depleter. Studies suggest about 40% of patients do get low. This may reflect the marginally normal people reacting faster than those with higher B12levels having enough to buffer the drug's effects. Remember, people can store B12 in the liver, and have a time delay in showing actual low values and symptoms. They can coast for a while on the stored B12, if B12 cannot be absorbed from animal sourced foods. I think this time factor is responsible for the long time it took for medicine to discover the negative effects of metformin and acid blocking drugs.

The acid blocking drugs for the stomach are more serious offenders IMO.