Vitamin B12 (Active)
Private Active Vitamin B12 testing in London for £129, measuring one biologically available B12 marker with results expected in around 2 days.
Turnaround time
2 days
Biomarkers count
1
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Overview of the Vitamin B12 (Active) Test
The Active Vitamin B12 blood test measures holotranscobalamin, the fraction of circulating Vitamin B12 that is bound to transcobalamin and available for uptake by cells.
The test assesses 1 nutritional biomarker: Vitamin B12 (Active).
Most Vitamin B12 circulating in blood is attached to carrier proteins.
Only the fraction bound to transcobalamin is readily available for cellular uptake.
This biologically available fraction is referred to as Active B12.
Active B12 can become reduced before Total B12 clearly falls below its reference range.
For this reason, it can provide useful additional information when Total B12 is borderline or symptoms strongly suggest deficiency.
Vitamin B12 is essential for DNA synthesis, normal red-blood-cell production and maintenance of the nervous system.
Deficiency can cause macrocytic or megaloblastic anaemia.
It can also produce neurological symptoms including tingling, numbness, balance disturbance and cognitive changes.
Importantly, neurological B12 deficiency can occur even without severe anaemia.
Risk factors include vegan diets without adequate supplementation, pernicious anaemia, autoimmune gastritis, gastric surgery, ileal disease, Metformin and prolonged acid-suppressing treatment.
Where the diagnosis remains uncertain, Methylmalonic Acid, Homocysteine or Intrinsic Factor Antibodies can provide additional information.
Recent B12 supplementation or injections can increase Active B12 significantly and should be included in interpretation.
What Does the Vitamin B12 (Active) Test Check?
The test measures biologically available Vitamin B12 circulating as holotranscobalamin. This test measures 1 biomarker.
Vitamin B12 (Active)
Measures holotranscobalamin-bound Vitamin B12, representing the circulating fraction readily available for cellular uptake.
Who May Benefit From the Vitamin B12 (Active) Test?
Active B12 can be particularly useful where Total B12 results are borderline or deficiency remains clinically possible.
People with a borderline Total Vitamin B12 result - Active B12 can provide additional information about cellularly available vitamin.
Vegans and people with limited animal-product intake - Dietary B12 deficiency risk can be increased.
People with tingling, numbness or neurological symptoms - B12 deficiency can damage peripheral nerves.
People with macrocytosis or megaloblastic anaemia - B12 is essential for normal red-cell production.
People with pernicious anaemia or autoimmune gastritis risk - Reduced intrinsic factor can impair B12 absorption.
People after gastric or ileal surgery - Normal absorption can be significantly reduced.
People taking Metformin or long-term proton-pump inhibitors - These medicines can contribute to lower B12 status in some people.
People monitoring B12 replacement - Results can provide information where interpretation accounts for supplementation timing.
How to Prepare
Do not stop medically necessary B12 replacement simply to obtain a lower laboratory value.
Recent treatment should instead be documented so the result can be interpreted correctly.
Symptoms and Reasons to Consider the Vitamin B12 (Active) Test
B12 deficiency can affect the blood and nervous system.
Persistent fatigue or weakness - Anaemia can reduce oxygen delivery.
Tingling or numbness in the hands or feet - Peripheral nerve dysfunction can occur with B12 deficiency.
Balance problems - Neurological deficiency can affect proprioception and gait.
Memory or concentration changes - B12 deficiency can affect neurological function.
A sore or smooth tongue - Glossitis can occur with nutritional deficiency.
Macrocytosis on a Full Blood Count - Enlarged red blood cells can prompt B12 and Folate testing.
A borderline Total B12 result - Active B12 can help clarify functional availability.
Neurological B12 deficiency can cause lasting damage if treatment is substantially delayed.
Progressive weakness, significant gait disturbance or new neurological symptoms require appropriate clinical assessment.
How to Book Your Vitamin B12 (Active) Test
The Active Vitamin B12 test can be booked privately for focused assessment of biologically available B12.
Choose the Vitamin B12 (Active)
Select the individual Active B12 blood test online.
Select your sample collection option
Choose an in-clinic blood draw or professional home or hotel phlebotomy where suitable.
Attend your appointment
A trained healthcare professional collects the required venous blood sample.
Laboratory analysis
Your serum undergoes measurement of Vitamin B12 (Active).
Receive your results securely
Your authorised result is delivered securely and can be interpreted alongside Total B12, Folate and related investigations.
When Will I Receive My Results?
The current live London Blood Tests page lists a turnaround of approximately 2 days after laboratory receipt for Vitamin B12 (Active).
The sample undergoes Active B12 analysis, laboratory quality-control procedures and result authorisation.
Understanding Your Results
A low Active B12 result indicates reduced biologically available Vitamin B12.
This can provide evidence of deficiency even when Total B12 is less clearly abnormal.
A result within range suggests adequate measured holotranscobalamin.
However, laboratory results should still be interpreted with symptoms and treatment history.
A high result is commonly seen after supplementation or B12 injections.
Unexplained high concentrations can occasionally require wider clinical assessment, but supplementation is by far the most common explanation.
Where deficiency remains uncertain, Methylmalonic Acid can provide information about intracellular B12-dependent metabolism.
Why Book With London Blood Tests?
London Blood Tests provides private Active B12 testing for focused nutritional and neurological assessment.
Measures biologically available B12 - Active B12 reflects holotranscobalamin available for cellular uptake.
Can detect earlier deficiency patterns - It can become abnormal before Total B12 in some people.
Useful with borderline Total B12 - The test can clarify uncertain results.
Relevant to neurological symptoms - Vitamin B12 is essential for normal nerve function.
Relevant to macrocytic anaemia - B12 is required for healthy red-blood-cell production.
Rapid laboratory turnaround - Results are expected approximately 2 days after laboratory receipt.
Professional blood collection - Clinic and suitable home or hotel appointments are available.
Clear pricing - The Vitamin B12 (Active) test costs £129.
Private Vitamin B12 (Active) Blood Test in London
London Blood Tests provides private Active Vitamin B12 testing for people requiring detailed assessment of B12 availability.
The test costs £129 and measures 1 nutritional biomarker.
Results are expected approximately 2 days after laboratory receipt.
The result is particularly useful where Total B12 is borderline or early deficiency remains possible.