Just to add to Patrick's reply - if you take a break of at least 3 days (preferably a week) from B12, before having a test done, you'll get a more accurate result on the test. (ie: not a false high result). Don't eat or drink anything for an hour after taking. Also I chew the sub-lingual - still works - and doesn't irritate my mouth. Don't expect a large jump in test levels - the number will increase slowly.