Originally Posted by mrsD

The B12 takes 72 hrs to be removed from the blood ....
This link says 6 days...but I have a pharmacology text that says 72 hrs. The 1/2 life is in the far right of this link and on other from medical sites on Google:
http://en.wikipedia.org/wiki/Vitamin_B12
Half life is one half of the total time it takes the vitamin to leave the serum.
This is another link:
http://toxnet.nlm.nih.gov/cgi-bin/si...rm+@DOCNO+2850

You have to discontinue it at least 3 days or more to get an accurate reading when taking supplements. Supplements being taken always give a higher than normal reading when tests are done, because the ranges were made with NO SUPPLEMENTS present.

I wouldn't expect a nurse to know what the absorption or excretion of B12 would be. Only about 13mcg are absorbed anyway from the GI tract. I have the studies on the B12 thread here.

People taking their B12 correctly orally often get levels of 1000 or more on testing after several months.