Active B 12 and just B12

[Spellweaver1312]

Can someone please explain the difference between B12 and active B12 please

[taka Administrator]

Hi Spellweaver1312

B12 can bind to several proteins in the blood including:

- haptocorrin (also known as transcobalamin I or R-factor)

- transcobalamin II (TCII or holoTC))

The normal B12 blood test measures the total B12 found in the blood - both the B12 bound to TCII and haptocorrin.

The active B12 test only measures the B12 bound to TCII. B12 needs to be bound to TCII to be able to bind to and be taken up by cells. This is a relatively new test and isn't very widely used yet.

It can vary quite a bit but ~80% of blood B12 is bound to haptocorrin and ~20% to TCII. Neither test will tell you if the B12 in the blood is actually being used by cells though...