What Holotranscobalamin measures
Holotranscobalamin reflects the active fraction of circulating vitamin B12 that is available for delivery into tissues.
Why this marker matters
When TCN2, MTRR, or B12-transport pathways look relevant, holotranscobalamin helps show whether delivery is part of the real-world picture.
When to check it
- when total B12 looks inconclusive
- when TCN2 or MTRR genes look relevant
- when fatigue or cognition issues persist despite intake or supplementation
How to interpret it
- use it with methylmalonic acid and symptom context
- interpret it as a delivery marker, not the whole B12 story
- avoid relying on total B12 alone
Where it fits in DNA follow-up
Holotranscobalamin is a direct bridge between B12 transport genetics and validation in practice.
Example interpretation
Your B12-transport pathway may deserve closer follow-up because holotranscobalamin can show whether usable B12 delivery is actually lagging.
Suggested companion markers: methylmalonic acid and homocysteine.