Should I Get My B12 Status Tested?
- Serum B12 Levels
- Homocysteine: Most Important Metabolite of B12 Status
- Methylmalonic Acid: Most Specific Test for B12 Status
- Homocysteine and MMA Tests Are Only Short-Term
- Recommendations on Getting B12 Status Tested
Vegans do not need to get their homocysteine or B12 levels checked merely because they are vegan. Rather, being vegan means that you should get a regular, reliable source of vitamin B12 from fortified foods and/or supplements. (Though if you've gone a month or so without a reliable source of B12, you should replenish your stores as described in Step 1 of the Recommendations.)
About 2% of people do not absorb B12 well. While this has nothing to do with being vegan, it is nice to know if you are such a person. You will not be able to tell unless you first have a reliable source of B12 for at least a few weeks before your B12 level is checked. Additionally, there are specific tests that directly measure B12 absorption.
If you get your B12 level checked, please note that eating seaweeds can falsely inflate B12 levels. Methods for determining B12 levels do not distinguish between B12 and some inactive B12 analogues. Many seaweeds contain a variety of inactive B12 analogues. Someone who is eating large amounts of seaweed may have serum B12 levels well above normal, but much of it could be inactive B12 analogues.
Blood homocysteine level is not a direct measure of vitamin B12 status because it is also affected by intake of, or metabolic problems with, folate and vitamin B6. However, homocysteine is the only known product of early B12 depletion that is thought to cause harm. For that reason, it is probably the most important marker of B12 status.
Some doctors recommend that all adults over age 45 have their homocysteine levels checked in order to catch a genetic predisposition to high homocysteine, which can often be successfully treated. It is best to ensure a reliable source of B12 and folic acid for a few weeks prior to the test. Otherwise, high homocysteine will not tell you whether you have a genetic predisposition, or if it was simply from a lack of B12 or folic acid in your diet. On the other hand, high homocysteine after a period of adequate B12 and folic acid intake shows that something else is a problem.
Methylmalonic Acid (MMA) builds up in the system when B12 status is poor. It is the most specific test for measuring B12 status because B12 is the only necessary co-enzyme needed to keep levels low. MMA can be measured in both the urine and the blood. If you want a snapshot of what your B12 status is at a given moment, then MMA is the test. The laboratory will tell you normal values for the specific test they are using. General parameters for MMA levels are listed here.
Just like for homocysteine, getting your MMA levels tested when not having a reliable source of vitamin B12 is probably a waste of time as there is a good chance it will be high, and it will only tell you what you already know: Everyone needs a reliable source of vitamin B12. In fact, I would see no reason to have MMA levels tested unless your serum B12 levels are normal, but you are still having symptoms of B12 deficiency. In this case, high MMA levels could indicate that you might have a B12 metabolism problem that can then be treated in some way. Of course, this should be done under the guidance of a physician.
Some people might think that instead of worrying about getting a reliable supply of B12, they will just have their MMA or homocysteine levels tested and if they are fine, then there's no reason to get a reliable supply of B12 for the time being. The problem with this is that you never know when you will hit the point at which MMA or homocysteine levels start to rise. They may stay low for years, months, or only days after they are tested and found to be healthy. At this time, there is no test that can tell you how long your B12 status will be adequate if you are not getting a reliable source of B12.
As mentioned above, for a variety of reasons, it is prudent for people to routinely have their homocysteine levels tested every 5 years after age 45. But unless you suspect a B12 absorption or metabolic problem, there is no reason to get MMA or B12 levels tested if you follow the recommendations here.