Holotranscobalamin (HoloTC)

The active, usable form of vitamin B12 in your blood, the earliest sign of B12 status.

Last reviewedJune 16, 2026

Serum

sample type

~3 mL

blood needed

~7 days

results in app

Any time of day

best timing

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On this page

Why test Reference ranges What you'll learn What affects it How testing works Sources FAQ

In short

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.

Vitamins & Minerals

Reviewed against DGKL reference practice.

Why test this?

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.

What is a normal result?

Aniva reads your result against research-backed ranges, not just the lab's wide normal. The reference shown below is specific to this biomarker.

Adult reference values as used by Aniva. Ranges are guidance and can vary by laboratory and method.

Group	Normal range
Adults	1720 to 8600 ng/L

Sources: 2011 AJCN HoloTC Review

Your Aniva report reads your result against these values together with your age, sex and the rest of your panel.

Ranges are guidance and vary by lab and assay, aligned with DGKL practice. Always read your result against your own lab's reference interval.

What insights will this test give you?

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.

What can affect this result?

What can skew the result

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.

Best interpreted with

Read alongside total vitamin B12, methylmalonic acid, homocysteine, and folate when assessing B12 status.

How is this tested?

Sample

Serum

Blood needed

~3 mL

Method

Immunoassay

Best timing

Any time of day

Sources. The evidence behind this

NIH Office of Dietary Supplements: Vitamin B12

NICE: Vitamin B12 deficiency guideline (NG239)

Serum holotranscobalamin versus total vitamin B12 as indicators of B12 status

Common questions

Which Aniva panels include this marker?

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These tests assess key vitamins for nerve, blood, bone, and energy function.