What is test for 'active b12'

[TFH1]

Hi I have been doing online research about PA. I have recently been diagnosed but am concerned about my daughter who suffers similar symptoms to me. I watched a clip on ITV's This Morning programme where a patient who had blood tests showing normal B12 levels was suffering with extreme deficiency symptoms. Dr Chris advises that people should make sure they ask for a blood test that measures ACTIVE B12 levels. Can anyone offer advice on this? Is this test likely to be offered by UK doctor if requested by patient?

[fbirder]

Your doc might, but probably won't.

B12 in the blood is bound to one of two proteins - transcobalamin (TC) and haptocorrin (TC). It's normally in the ratio of about 4:1 HC-B12 to TC-B12. Only the TC-B12 can enter the cells and partake in the reactions where B12 is important. So the TC-B12 is called Active B12, or holotranscobalamin.

Some people make a big deal of the fact that the serum B12 test measures both forms and that it greatly overestimates the 'true' B12 level. This is wrong. The normal range for Active B12 tests is normally about 4 times lower than the serum test - because the people who develop the tests aren't stupid.

It's like counting a flock of sheep that is supposed to have 100 sheep in it. You can count heads, or you can count legs. If you get a value of between 95 and 105 heads then you've got about the right number of sheep. Similarly, a value of between 350 and 440 legs means you have about the right number.

You may have noticed that the range for legs actually converts to between 88 and 110 sheep. That's because counting heads is, inherently, more accurate than counting legs in a milling flock.

It's the same with the Active B12 test - it is both more accurate and more precise than the serum test. You are less liable to get false positives (or false negatives) - at least that's what the test developers tell us. This is, as far as I can tell, the only reason to ask for the active test. And there's not much point if a serum test has already shown you to be deficient.

Some have postulated that some people have much less than 20% of the circulating B12 as TC-B12, with almost all of it as HC-B12, and that this is a good reason to have the active test. I don't think I've ever seen any orproper study that has shown this to be a thing.

[TFH1 in reply to fbirder]

Thanks for the reply - I really appreciate your taking the time to explain. I was asking on behalf of my daughter whose bloods show a B12 of around 400 but who is exhausted. I was confused after watching this woman on This Morning who also had normal blood test results but her active b12 was very low. It's all very confusing.

[fbirder in reply to TFH1]

Yes, it is possible to have a 'normal' serum B12 and low Active B12. That's mainly because the serum test isn't reliable (you can test the same sample twice and get results that differ by 10-20%) and because they need to set the 'normal' range high enough to minimise false negatives.

That's why there's really only one good test for a B12 deficiency - that's how you respond to B12 injections.

[TFH1 in reply to fbirder]

Yes - we are considering self injecting to see if it helps - she's a young active woman, 20 years old at University and constantly struggling with exhaustion as well as other symptoms. Many of her friends are medics and could adminsister a jab. Any recommendation of best place to buy the b12 ampoules gratefully received.

[fbirder in reply to TFH1]

I buy my B12 from versandapo.de - versandapo.de/vitamin-b12-d...

But if you're just going to try it out I would just buy 10 ampoules - versandapo.de/vitamin-b12-d...

If you pay using PayPal or Amazon Pay then it can be much easier.

[Colorado76 in reply to fbirder]

Do you know if they ship to the US? Does this include the needles too? I couldn't tell from the pic and description... Thanks!

[fbirder in reply to Colorado76]

I don't think they do ship to the US. Getting hydroxocobalamin in the states isn't easy. Cyanocobalamin should be much easier to source. There are a couple of threads on here about it.

It definitely doesn't include syringes and needles.

[Colorado76 in reply to fbirder]

Thanks... that's too bad that just getting a ' vitamin' , a life saving vitamin is hard to get in the form you want. I'd much prefer the methylcobalamin. Thanks fbirder.

[fbirder in reply to Colorado76]

There's no reason why methylcobalamin should be any better than hydroxocobalamin or cyanocobalamin.

b12science.com/B12Science/D...

[Colorado76 in reply to fbirder]

Wow, that's so interesting! I was told methylcobalamin was better because it was the "purest" form of B12 and that our bodies had to work harder to get rid of the cyanide in the synthetic B12 form. Thank you for the scientific clarification!

[TFH1 in reply to fbirder]

Thanks that's really helpful