I've had a couple of PMs and read a few posts about these two tests - especially MMA. So I thought I'd write my thought down in a separate post.
What are MMA and homocysteine.
B12 does lots of things in the body. Two of the more important (and ones we can actually test for) are:
Methylmalonic acid, combined with something called CoA is converted to succinyl CoA by an enzyme that requires adenosylcobalamin to work. Succinyl CoA is an important chemical in the biochemical process that 'burns' glucose to produce energy (You may recall from school studying Krebs cycle - or the citric acid / tricarboxylic acid / TCA cycle). A lack of B12 means that this reaction doesn't proceed as fast as is ideal, resulting in a lack of energy and a buildup of methylmalonic acid.
The other important process is the methylation of homocysteine to form the amino acid methionine in a process that requires methylcobalamin and methylfolate. If B12 is low then homocysteine builds up - with possible bad consequences.
The two tests are both involved and expensive, so GPs may be loath to give them. The homocysteine test needs to be run within 2 hours of the sample being taken.
Why test for MMA and/or homocysteine?
We all know that the blood tests for B12 aren't too useful. Many people have high serum levels of B12, yet still have symptoms of B12 deficiency. There are many possible reasons why this may be so. One reason is that the B12 isn't actually getting to the places in the cell where it's needed. If this is the case then levels of MMA and/or homocysteine will be raised. So a raised level of either of these might persuade the GP that you have functional B12 deficiency and that you do need more frequent injections.
When should you test?
Testing for these two markers should, ideally be done before B12 supplementation - to show that B12 deficiency is actually the problem. I believe it should also be done during supplementation - to show that the B12 deficiency has been fixed.
If you're trying to show that your symptoms are due to a functional deficiency then you really need to demonstrate that you have high levels of one or both of these markers while on supplements. Ideally you want to leave a sufficient gap since your last jab for you to start suffering the symptoms again. So if you normally inject weekly, because you start feeling bad after 8 to 10 days, then testing the markers after 12 to 14 days should show raised levels if you are functionally deficient.
What if I test normal?
I need to inject weekly. If I forget then, by day 9, I get very fatigued. When I was going for an MMA test I waited 16 days between jabs - and I was wrecked. The test was normal. So I'm not functionally deficient. So why do I need weekly jabs? Two reasons - the haematologist reckons it's a placebo effect, and he's entitled to his opinion. Personally, I think it's a cop-out and there's something more complicated going on.
Because I've not had a homocysteine test I'm not sure if there's anything amiss there. I keep asking and they keep saying they'll do one - but no results forthcoming.
Remember I said that these are two of the processes that B12 is involved in. Well, it's my opinion that B12 does a lot more than 2 things. We know about some (it's involved with monoamine neurotransmitters) but I'd be surprised if there weren't others. There's some research talked about on the PAS site that I think is looking for further markers to investigate the possibility of other problems in people with high levels of B12 but low levels of life quality.