What is Holotranscobalamin?
the active form of B12
Holotranscobalamin measures the biologically active part of B12 - the fraction that cells can actually take up. It is a more sensitive measure than total B12.
Only about 20 percent of blood B12 is active. Holo-TC measures this fraction and is useful in borderline cases where total B12 is near the threshold.
Test facts
- Unit
- pmol/L
- Sample
- Serum
- Fasting
- No fasting needed
- Turnaround
- 3 days
What does low Holotranscobalamin mean?
Low holo-TC points to functional B12 deficiency even when total B12 is normal.
What does high Holotranscobalamin mean?
High holo-TC is not clinically problematic.
Panels that measure Holotranscobalamin
- Vitamins & Minerals Full
More markers in the same area
Launching in Stockholm in 2026.
Want to know when you can order?
This is general information about the marker, not an assessment of your values and not medical advice. Last updated: May 2026.