Active Vitamin B12 (Holotranscobalamin)

Overview

Active Vitamin B12 (Holotranscobalamin) is the bioavailable portion of vitamin B12 that the body can immediately use. Unlike total vitamin B12, which includes forms of B12 stored in the liver but not actively used by the body, active B12 is bound to the transport protein transcobalamin, delivering it directly to cells. This bioactive form is crucial for several vital processes, such as DNA synthesis, the formation of red blood cells, and maintaining neurological health. Think of it as the courier that delivers vitamin B12 right to where it’s needed, helping the body perform essential functions to keep you healthy and energetic. By measuring active B12, healthcare professionals can assess whether the body has sufficient levels of this vital nutrient for immediate use, even if total B12 appears normal.

Testing Levels:

• High (250 pmol/L) - Elevated active B12 levels are rare but can occur. High levels may be associated with certain conditions such as liver disease, kidney dysfunction, or certain types of leukaemia. In these cases, elevated B12 is not caused by excessive intake but is often due to a release of stored B12 into the bloodstream, a sign that these organs are not functioning properly. It’s a marker that may need further investigation to identify underlying health conditions.
  
  
• Mid - Active B12 levels within the reference range indicate that your body has a sufficient amount of bioavailable vitamin B12 to support normal physiological functions, such as maintaining healthy blood cells and nerve function. This balance suggests effective dietary intake and absorption, contributing to overall well-being and energy levels.
  
  If active B12 levels are near the upper limit but still within the reference range, it’s generally not a cause for concern. This can indicate good nutrient status, especially in individuals who are supplementing B12 or consuming a diet high in B12-rich foods like meat, fish, and dairy. However, it’s essential to monitor B12 levels over time if there are underlying health concerns, particularly with liver or kidney function.
  
  Active B12 levels close to the lower limit may signal the beginning stages of a deficiency, even if total B12 levels are within the normal range. This can lead to symptoms such as fatigue, mild cognitive issues, and a general feeling of weakness. At this stage, it’s vital to take action by increasing B12 intake through dietary sources or supplementation to prevent deficiency from worsening.
  
  
• Low (25 pmol/L) - When active B12 levels fall below the reference range, it indicates a deficiency, even if total B12 levels are normal. Low active B12 can lead to anaemia, nerve damage, and cognitive impairment. Symptoms may include tingling in the hands and feet, difficulty concentrating, memory problems, and tiredness. Immediate intervention through B12 supplementation or treatment for absorption issues is often required to avoid long-term health complications.

Why We Test Active Vitamin B12 (Holotranscobalamin)

Testing active B12 provides a more accurate measure of B12 availability in the body than total B12. It helps identify deficiencies that can affect energy levels, cognitive function, and overall health. This test is particularly important for individuals at risk of B12 deficiency, such as those following plant-based diets, older adults, or individuals with digestive disorders. Early detection of low active B12 levels allows for timely intervention, preventing potentially serious complications like anaemia and neurological damage.

What Affects It

Several factors can influence active B12 levels. Nutritional intake, particularly in people with vegan or vegetarian diets, can lead to lower levels due to limited B12 from plant-based sources. Digestive health also plays a role: conditions like pernicious anaemia or gastrointestinal disorders such as Crohn's disease and coeliac disease can impair absorption. Medications such as proton pump inhibitors (PPIs) or metformin may also decrease B12 absorption. Additionally, as we age, our ability to absorb B12 naturally declines, making older adults more susceptible to deficiencies.

How to Improve

If active B12 levels are low or approaching the lower limit, dietary changes or B12 supplementation can be beneficial. For those at risk of deficiency (vegans, older adults), increasing B12-rich foods (e.g., meat, dairy, fortified cereals) or taking oral or injectable supplements can help. If the levels are too high, it’s important to assess liver and kidney health, as high B12 may be a sign of underlying issues rather than dietary intake. Regular monitoring and medical advice will help guide appropriate adjustments.

Common Name: Active Vitamin B12