Understanding What Is a Good Level of Active B12

November 20, 2025 •

4 min read

Active B12, or holotranscobalamin, is the metabolically active form of the vitamin, representing only 6% to 20% of your total B12 and is considered a more reliable indicator of true B12 status. A good level of active B12 ensures your body can utilize this essential nutrient for proper nerve function, DNA synthesis, and red blood cell production.

Quick Summary

This article details what constitutes a good level of active B12, explains the difference between active and total B12 tests, outlines deficiency symptoms, and provides methods for maintaining optimal levels.

Key Points

Active B12 is Bioavailable: Active B12, or holotranscobalamin, is the form of vitamin B12 that your body's cells can actually use.
Good Levels are >70 pmol/L: A healthy or sufficient level of active B12 is typically considered to be above 70 picomoles per liter (pmol/L).
Indeterminate Range Needs Investigation: Levels between 25-70 pmol/L are in an indeterminate range and may indicate a possible deficiency that warrants further testing.
Low Levels Cause Varied Symptoms: A deficiency in active B12 can cause symptoms ranging from extreme fatigue and lethargy to neurological issues like tingling and memory problems.
High Levels May Indicate Underlying Issues: Unexplained high active B12 levels, not caused by supplements, can sometimes point to underlying liver disease or other serious conditions.
Supplementation Can Boost Levels: For those with a deficiency, increasing levels can be achieved through a diet rich in animal products or fortified foods, or through supplements and injections.

Active vs. Total B12: Understanding the Difference

When you get a blood test for vitamin B12, labs can measure two different things: total B12 (serum cobalamin) and active B12 (holotranscobalamin or holoTC). Total B12 measures both the active and inactive forms of the vitamin, which can sometimes be misleading. Approximately 80% of your total B12 is bound to a protein called haptocorrin, rendering it inactive and unusable by the body's cells. The remaining 20% or less is active B12, bound to a protein called transcobalamin, and is available for cellular uptake. Because active B12 is the fraction your body can actually use, it is considered a more specific and earlier marker for deficiency than total B12, especially in borderline cases.

What Is a Good Level of Active B12?

Reference ranges for active B12 can vary slightly between different laboratories, so it is crucial to discuss your results with a healthcare provider. However, a general guide to interpretation includes:

Deficient: Below 25 pmol/L. A result in this range indicates a clear shortage of the bioavailable vitamin, and supplementation is likely necessary.
Indeterminate/Suboptimal: Between 25-70 pmol/L. In this range, deficiency is possible, even if a total B12 test appears normal. Additional testing, such as methylmalonic acid (MMA), may be recommended.
Normal/Sufficient: Above 70 pmol/L. This level indicates that your body has an adequate supply of active B12 for normal cellular function.
Optimal: While the 'normal' range is wide, some data suggests that levels below 70 pmol/L could be suboptimal for some individuals, even without overt symptoms. For overall wellness, maintaining levels well within the sufficient range is generally desirable.

Symptoms of Low Active B12

Because low active B12 indicates that less of the vitamin is available for your cells, symptoms can appear even if your total B12 appears normal. These symptoms often develop gradually and can affect multiple bodily systems.

Common physical and psychological symptoms:

Extreme fatigue and weakness
Lack of energy (lethargy)
A sore, red, and swollen tongue (glossitis)
Mouth ulcers
Pale or yellowish skin
Weight loss and decreased appetite
Feeling irritable or depressed

Neurological symptoms, which can be more severe:

Pins and needles (paraesthesia) in the hands and feet
Numbness or tingling
Difficulty with memory, confusion, and cognitive impairment
Vision problems
Problems with balance and walking
Changes in thinking, feeling, and behavior

When High Active B12 is Cause for Concern

High B12 levels resulting from dietary intake or supplementation are usually harmless, as the body excretes excess water-soluble vitamins in the urine. However, naturally high levels (unrelated to supplementation) can sometimes indicate an underlying medical condition. Conditions associated with high B12 levels include:

Liver disease (such as cirrhosis or hepatitis)
Certain myeloproliferative disorders (blood cancers)
Kidney disease
Certain tumors

If you have naturally high B12 levels, a healthcare provider will investigate the underlying cause rather than treat the B12 level itself.

How to Increase Your Active B12 Levels

Increasing your active B12 levels typically involves dietary changes and, in many cases, supplementation. For dietary B12, it is found naturally in animal products.

Foods high in vitamin B12 include:

Beef liver and other organ meats
Clams and salmon
Beef and poultry
Eggs and dairy products like milk, yogurt, and cheese
Fortified foods, such as breakfast cereals, nutritional yeast, and plant-based milks

For those with diagnosed deficiencies or malabsorption issues, healthcare professionals may recommend supplements or injections. Oral supplements are often effective, but injections may be necessary for severe cases or those with impaired absorption.

Comparison: Active B12 (HoloTC) vs. Total B12 Test


Feature	Active B12 (Holotranscobalamin)	Total B12 (Serum Cobalamin)
What it measures	Only the B12 that is biologically available for cells.	Both the active and inactive forms of B12.
Sensitivity	More sensitive for detecting early or borderline deficiencies.	Less sensitive; can miss some cases of deficiency, especially in early stages.
Accuracy	Better reflects the body's actual B12 status at the cellular level.	Can sometimes show normal results even when a functional deficiency exists.
Stability	Considered stable during pregnancy, making it useful in certain contexts.	Less reliable during pregnancy due to hormonal changes.
Prevalence of use	Less commonly used due to higher cost and limited availability.	More widely used and readily available, but with limitations.
Indication	Low levels indicate that the body's store of usable B12 is becoming depleted.	Provides an overall snapshot but can be misleading in certain scenarios.

Conclusion

Understanding what is a good level of active B12 is essential for accurately assessing your vitamin B12 status. Unlike the total B12 test, which measures both active and inactive forms, the active B12 (holotranscobalamin) test offers a more precise indication of the vitamin available for your cells. A sufficient level is considered to be above 70 pmol/L, while levels between 25-70 pmol/L may indicate a suboptimal status requiring further investigation. A persistent deficiency can lead to a range of physical, psychological, and neurological symptoms. While high levels are rarely a concern from diet or supplements, they can signal underlying issues if unexplained. Consulting a healthcare professional for proper testing and guidance on diet and supplementation is the best way to ensure optimal B12 health. For more on B12 absorption, see the NIH factsheet for health professionals.

Frequently Asked Questions

Total B12 measures both active and inactive forms of the vitamin, while active B12 (holotranscobalamin) specifically measures the form that is available for cellular use. Active B12 is considered a more accurate indicator of true B12 status.

Levels of active B12 below 25 pmol/L are generally considered deficient and require attention. Persistent, untreated deficiency can lead to severe and irreversible neurological damage.

Yes, it is possible. This is why active B12 testing can be a more sensitive and specific marker, as a normal total B12 reading can sometimes mask a functional deficiency.

Common causes include dietary insufficiency (especially in vegans/vegetarians), poor absorption due to conditions like pernicious anemia or Crohn's disease, and certain medications.

High levels from food or supplements are not usually a concern because the body excretes the excess. However, naturally high levels (not from supplementation) can be a sign of an underlying medical condition, and you should consult a doctor.

For diagnosed deficiency, B12 injections or high-dose oral supplements are the fastest way to restore levels. Dietary changes are also important for long-term maintenance.

Animal products like meat, fish, eggs, and dairy are rich in B12. Vegans and vegetarians can get B12 from fortified foods like cereals, plant-based milks, and nutritional yeast.