The active, usable form of vitamin B12 in your blood, the earliest sign of B12 status.
Holotranscobalamin (HoloTC), often called active B12, is the portion of vitamin B12 in your blood that is bound to a carrier protein called transcobalamin. This is the fraction that cells can actually take up and use.
Because it measures the usable part of B12, HoloTC can be a more sensitive early marker of B12 status than total vitamin B12, which also includes B12 that cells cannot access.
Vitamin B12 is needed for nerve health, red blood cell production, and DNA synthesis. Because HoloTC reflects the B12 that cells can use, a low value can flag a developing deficiency early, before total B12 falls.
Testing active B12 is useful when total B12 is borderline or when symptoms suggest deficiency despite a normal total level. It is often read together with markers like methylmalonic acid and homocysteine.
Aniva reads your result against research-backed ranges, not just the lab's wide normal. The reference shown below is specific to this biomarker.
Measured in serum. Ranges are guidance and vary by laboratory and method.
| Status | Holotranscobalamin |
|---|---|
| Likely deficient | Below 25 pmol/L |
| Indeterminate | 25 to 50 pmol/L |
| Likely sufficient | Above 50 pmol/L |
Some laboratories use slightly different cutoffs, for example treating below 35 pmol/L as low. Confirm the exact interval with the reporting laboratory.
You learn whether your active B12 is low, borderline, or adequate. A low result suggests poor B12 delivery to your cells, sometimes even when total B12 looks normal. This can prompt further testing, such as methylmalonic acid, to confirm a functional deficiency.
Recent B12 supplementation or injections raise levels. Results in the indeterminate range often need follow-up with methylmalonic acid to clarify whether there is a true functional deficiency. Kidney function can influence related markers used alongside HoloTC.
Read alongside total vitamin B12, methylmalonic acid, homocysteine, and folate when assessing B12 status.
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