Serum vs Active

[ella2b]

Hello, I had bloods done via medichecks and came out as 89ng/l active b12 on 23/12/19.

Spoke to GP had serum b12 2/1/20 result was 344 ng/L. Is the issue here that serum will be all b12 and not just the active? Where do I go from here? Thank you.

[fbirder]

The B12 in your blood is bound to one of two proteins - transcobalamin (TC) and haptocorrin (HC) with most of it (about 80%) being bound to HC. Only the TC-B12 can enter the cells where it does its various jobs. This is called 'active' B12.

The serum test measures both TC-B12 and HC-B12. The 'active' test measures just the TC-B12. So, you would expect the serum test to give a value about five times higher than the active test. That is why the normal range of the serum test is about 5 times higher than the active test.

You might ask - "Why bother with the active test then?". The answer is that it is supposed to be more accurate and more precise than the serum test. WIth the latter you could measure the same sample twice and get results that varied by about 10 to 20%.

If you have a serum test that is in the grey area then an active test may be useful to give you a better idea if you are deficient or not.

Both your tests give results well into the normal range. If you've not been taking supplements that suggests you aren't B12 deficient.

[ella2b in reply to fbirder]

Thank you

[Sleepybunny]

Hi,

My understanding is that none of the tests used to help diagnose B12 deficiency eg serum B12, Active B12 ( also known as HoloTC/Holotranscobalamin), MMA, Homocysteine are totally reliable.

There was a recent post about this on forum which I'll try to find a link to. The article mentioned was a review of the problems of diagnosing B12 deficiency from Mayo Clinic Proceedings: Inn.Qual.Out. June 2019 Vol 3 (2) pp 200-214

Retteacher , have you got a direct link to above article? Thanks.

This flowchart from a UK document indicates that doctors should consider continuing B12 treatment in patients symptomatic for B12 deficiency even if secondary tests such as Active B12, MMA, Homocysteine are negativenormal range.

Flowchart from BSH Cobalamin and Folate Guidelines

stichtingb12tekort.nl/weten...

Flowchart outlines process for diagnosing PA and Antibody Negative PA in UK

BSH Cobalamin and Folate Guidelines

(link to complete guidelines, Active b12 test plus other tests are mentioned)

b-s-h.org.uk/guidelines/gui...

Letters to GPs about B12 deficiency

b12deficiency.info/b12-writ...

Point 5 in above link is about being symptomatic for B12 deficiency with an in range B12 result. Some of the info is specific to UK.

Articles from Dutch B12 website (English language)

"The serum B12 test is often not sufficient to diagnose a deficiency"

stichtingb12tekort.nl/weten...

"Serum B12"

stichtingb12tekort.nl/weten...

"Methylmalonic acid"

stichtingb12tekort.nl/weten...

"Misconceptions about a B12 deficiency"

stichtingb12tekort.nl/weten...

I had multiple typical symptoms of B12 deficiency including neurological symptoms, with most serum B12 results between 300 - 500ng/L.

I'm trying to say in a very long winded way that it's still possible to have B12 deficiency with normal range test results.

I wrote a very detailed reply on another forum thread which has links to B12 books, B12 websites, B12 documents and other B12 info. I suggest you have a look as hopefully some of the info will be of use.

healthunlocked.com/pasoc/po...

I am not medically trained.

[ella2b in reply to Sleepybunny]

Thank you