What is an active blood test.

[Belsfield]

What is an active blood test.

[Gambit62 Administrator]

There are two types of serum B12 test - one is total serum B12 and the other is active B12.

Generally active B12 (B12 bound to a protein called TC which is needed to allow it to pass into cells) is 20% of total serum B12 so no really point in doing both as a matter of routine. The active B12 test is also known as holo-T (mainly in US).

active B12 is a more accurate that serum B12 (which is only accurate to within 20%)

[Belsfield in reply to Gambit62]

Thanks.

[fbirder]

In the blood, B12 is bound to one of two proteins - haptocorrin (HC) or transcobalamin (TC). Only the TC-B12 can enter the cell, this is known as 'Active' B12 (or holotranscobalamin, holo-TC). About one-fifth of the total B12 in the blood is TC-B12. Nobody is quite sure of the purpose of HC-B12.

You can measure the amount of B12 by looking at TC-B12 (the 'Active' B12 test) or the combination of both of them (the serum test). Because there is less TC-B12, the 'normal' range for it will be about one-fifth the normal range of the serum test.

The Active B12 test is supposed to be better than the serum B12 test. The latter is neither precise, nor accurate. You could measure the same sample twice and get answers that differ by more than 10%.

[Belsfield in reply to fbirder]

Thanks.

[Sleepybunny]

Hi,

Links about Active B12 test

active-b12.com/frequently-a...

viapath.co.uk/our-tests/act...

I think Active B12 (holotranscobalamin) is mentioned in this UK document

BSH Cobalamin and Folate Guidelines

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