Blood test

[networker]

I'm new to this site and wonder if anyone could shed some light on a question I have .

Got an appointment with a haematologist pending,going to request a MMA blood test and was wondering would taking B12 supplements affect the results of this test I've recently had a B12 serum test which showed my B12 to be high . By the way went to my GP to request MMA test and he'd never heard of this test.

[fbirder]

What do you want the test to show?

If it's to show that you have a functional B12 deficiency, where the B12 isn't working even though there's plenty in the blood, then you want to keep supplementing.

If it's to confirm that you have a deficiency of B12 then you really need to stop supplementing for several months beforehand.

[networker in reply to fbirder]

Been off the supplements for 3months and B12 was 680 I've started having more episodes than I've had in the last 5 years since stopping the supplements gone back on the B12 supplements now was just unsure if I manage to get an MMA test would the supplements affect the test just want to have someone tell me there is a problem with my B12 uptake one way or another .. If haematologist doesn't give me tha MMA test has anyone got any suggestions for getting it done privately ...

[Secondchance]

Taking B12 supplements will most likely make MMA test pointless by skewing results in favour of showing low MMA and therefore disproving functional B12 deficiency. I have read here a number of times that people thought they wasted their money by testing these after supplementing. If you think you have high serum B12 but your body is not using it have you also considered active B12/holotranscobalamin test available at St Thomas hospital? There is no perfect test. If this test is borderline they then suggest doing MMA/homocysteine. Homocysteine is also high with folate deficiency though.

[fbirder in reply to Secondchance]

Taking B12 supplements will most likely make MMA test pointless by skewing results in favour of showing low MMA and therefore disproving functional B12 deficiency.

A functional deficiency means that the cell itself is deficient despite high serum levels of B12. So testing for a functional deficiency with low serum levels of B12 would be pointless - you'd be showing that the B12 wasn't doing a proper job, but that almost certainly because there's no B12 to do the job.

It would be like trying to test a fuel injection system on a car by seeing if the engine runs. If it doesn't run despite there being fuel in the car then there could be a problem with the injection system. If you try testing without any fuel in the car then you've no idea if the injection system is working or not.

The holotranscobalamin test will only show the amounts of B12 that is capable of getting into the cell. If it's low, despite high serum B12, then that would cause high MMA levels. But if the holotranscobalamin comes back high then you could still have a functional deficiency if the active B12 either isn't getting into the cell, or can't work properly once it gets in.

As you say, there is no perfect test - even serum MMA can give a falsely high reading in people with kidney problems. But MMA and homocysteine are the best tests for a functional deficiency.