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Vitamins

Holotranscobalamin Test

Holotranscobalamin measures the biologically active B12 available to your cells and is considered the earliest marker of B12 depletion. Monitoring this marker may help detect changes in your B12 status before standard tests.

Doctor's Assessment Included

When is this value abnormal?

Decision limits per result, in pmol/l
Result Value (pmol/l)
Low < 20
Borderline 20–40
Sufficient ≥ 40

Cut-off values differ between laboratories (Saltro 20/40 pmol/l; elsewhere 25/45, or 35/50 internationally). These bands follow Saltro. Active B12 is not suitable for monitoring during supplementation.

Source: Saltro

Reference ranges may vary between laboratories. When you order a test, a BIG-registered doctor assesses your personal results in context. For treatment decisions, discuss your results with your GP.

Holotranscobalamin: what this test measures

This test measures holotranscobalamin (holoTC), the complex of vitamin B12 bound to transcobalamin II. This represents roughly 10-30% of circulating B12 but is considered the only form available for cellular uptake and metabolic use.

Holotranscobalamin: why this value matters

Early detection of B12 depletion through holotranscobalamin testing may allow you and your healthcare provider to take action before deficiency symptoms appear. This proactive approach could help maintain your energy, mood, and cognitive function.

Holotranscobalamin: how the blood test works

Referral
No GP referral needed. After the order we arrange the referral through ZorgDomein, within one business day; orders after 17:00 or at the weekend start on the next business day. ZorgDomein emails a barcode, and that barcode is what the draw site needs.
The draw
A blood draw from a vein in the arm, at a partner laboratory's draw site. No home kit, no finger prick.
Which test
on its own €49,-
Where
650+ draw sites run by independent laboratories across the Netherlands. Draw sites

Holotranscobalamin: when is testing worthwhile?

Testing may be recommended when total B12 results are borderline, if you have risk factors for B12 deficiency, or when your healthcare provider wants a more sensitive assessment of your B12 status. It can help clarify ambiguous total B12 results.

Holotranscobalamin: symptoms of a high or low value

Low Levels

Some people with low holotranscobalamin may experience early signs of B12 deficiency including subtle fatigue, mild cognitive difficulties, and slight mood changes. These symptoms may appear before more obvious signs of deficiency develop.

High Levels

Elevated holotranscobalamin levels are generally not associated with specific symptoms. However, very high levels may occasionally be seen in certain medical conditions and should be discussed with your healthcare provider for proper interpretation.

Holotranscobalamin: lifestyle and this value

Supporting healthy B12 levels through diet may include consuming animal products such as meat, fish, eggs, and dairy. Those on plant-based diets should consider discussing B12 supplementation with their healthcare provider to maintain adequate stores.

Holotranscobalamin: frequently asked questions

How is holotranscobalamin different from active B12?

Holotranscobalamin and active B12 measure the same thing — the biologically active form of vitamin B12 bound to transcobalamin II. They are essentially the same test, sometimes referred to by different names in different clinical settings.

When would my doctor order this test instead of total B12?

This test is often ordered when total B12 results are borderline or inconclusive, or when a more sensitive early detection of B12 depletion is desired. It may provide clearer information about your body's functional B12 availability.

Can holotranscobalamin detect deficiency earlier than other tests?

Holotranscobalamin is considered one of the earliest markers to change when B12 stores begin to deplete. It may detect insufficiency before total B12 levels fall below reference ranges, potentially allowing for earlier intervention.

Holotranscobalamin: sources

  1. Saltro (Unilabs). Actief vitamine B12 (holotranscobalamine): afkapwaarden. Geraadpleegd 14 juli 2026. (retrieved 2026) saltro.nl

Tests with related values

These panels measure values from the same category as this marker.

Whoop

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Whoop

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A 54-biomarker women's health panel inspired by the WHOOP Women's Health Panel — fertility, cycle and thyroid hormones plus a complete metabolic and nutrient base.

Complete Blood Count (CBC) ALP (Alkaline Phosphatase) ALT (Alanine Aminotransferase) AST (Aspartate Aminotransferase) Albumin Total Protein Bilirubin (Total) ApoB (Apolipoprotein B) Total Cholesterol LDL Cholesterol HDL Cholesterol Triglycerides Lipoprotein(a) Urea (BUN) Creatinine eGFR (Estimated Glomerular Filtration Rate) Calcium Bicarbonate Chloride Sodium Potassium Magnesium Cortisol DHEA-S Estradiol (E2) FSH (Follicle Stimulating Hormone) LH (Luteinizing Hormone) SHBG (Sex Hormone Binding Globulin) Total Testosterone Free Testosterone TSH (Thyroid Stimulating Hormone) Glucose (Fasting) HbA1c (Glycated Hemoglobin) Insulin (Fasting) HOMA-IR CRP (C-Reactive Protein) Homocysteine Ferritin Iron (Serum) Transferrin Transferrin Saturation Vitamin D (25-OH) AMH (Anti-Müllerian Hormone) Progesterone Prolactin TPO Antibodies Free T3 (Triiodothyronine) Free T4 (Thyroxine) Leptin Vitamin B12 Folate (Folic Acid) Phosphorus Bilirubin (Direct) Bilirubin (Indirect) Cholesterol/HDL Ratio Non-HDL Cholesterol LDL/HDL Ratio
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InsideTracker

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An InsideTracker blood test with 35 biomarkers: heart, hormones, metabolism, inflammation, recovery and iron status. Measured in the Netherlands.

SHBG (Sex Hormone Binding Globulin) TSH (Thyroid Stimulating Hormone) ALT (Alanine Aminotransferase) LDL Cholesterol GGT (Gamma-Glutamyl Transferase) Cortisol DHEA-S Estradiol (E2) Free Testosterone Total Testosterone Folate (Folic Acid) Vitamin B12 Calcium Ferritin Iron (Serum) Magnesium Potassium Progesterone Sodium Transferrin CRP (C-Reactive Protein) Glucose (Fasting) HbA1c (Glycated Hemoglobin) ApoB (Apolipoprotein B) HDL Cholesterol Total Cholesterol Albumin AST (Aspartate Aminotransferase) Vitamin D (25-OH) Insulin (Fasting) Leukocyte Differential Creatine Kinase (CK) Transferrin Saturation Triglycerides Basic Blood Count HOMA-IR Cholesterol/HDL Ratio Non-HDL Cholesterol LDL/HDL Ratio
€399,-

Medical reviewer

Medical standards

Dr. Naimi oversees the medical standards behind our content and assessments.

Medical policy
CIBG Ministerie van Volksgezondheid,
Welzijn en Sport Official BIG registration BIG 49928676701 Opens in a new tab

Holotranscobalamin

€49,-