Is there a test for vitamin B12 deficiency?

    Written by:
    Megan Michaux

    Fact-checked

    by:

    Nick Milazzo
    Last Updated: May 16, 2025

    A blood test can determine vitamin B12 deficiency; a level below 148 pmol/L indicates deficiency, and levels between 148–221 pmol/L are considered intermediate. If levels are low, treatment should begin, but further testing may be necessary for people in the intermediate range or if symptoms persist despite normal B12 levels.

    To check for vitamin B12 deficiency, a test can be done to look at the level of B12 in the blood. A level below 148 pmol/L is considered low, and 148–221 pmol/L is intermediate.[1] The result of this test is considered a fairly accurate representation of the amount of B12 in the body. If it is low, treatment should be initiated. If it is high, or on the high end of the normal range, it is likely not a concern.

    The intermediate range has become more difficult to interpret. A new understanding that a level of vitamin B12 in the lower end of the normal range could be associated with symptoms means that we now have something called subclinical vitamin B12 deficiency. In these instances, further testing might be a good idea. Testing for methylmalonic acid or homocysteine levels might help support the diagnosis of B12 deficiency if they come back as high.[2][1]