Vitamin B12 blood test with antibodies
Vitamin B12 blood test with intrinsic factor and gastric parietal cell antibodies, as well as folic acid, full blood count and homocysteine. It is designed to investigate whether B12 deficiency may be due to autoimmune gastritis or pernicious anaemia, a cause that impairs absorption and changes the subsequent follow-up.
No prescription or appointment needed
Results in 5-7 working days
Includes: Vitamin B12 · Folic acid · Full blood count · Homocysteine · Gastric parietal cell antibodies · Intrinsic factor antibodies. See what each one measures
What it is for
It is used to investigate two questions from the same sample. On one hand, whether there is laboratory evidence of vitamin B12 deficiency. On the other, whether there are antibodies that support an autoimmune origin and explain insufficient absorption.
Identifying the cause matters. A dietary deficiency can be corrected by adjusting intake and supplementation, whereas autoimmune gastritis usually requires long-term replacement and specific medical follow-up. The antibodies give guidance, but they must be interpreted together with B12, symptoms and, where appropriate, a digestive assessment.
When it is recommended
- Confirmed vitamin B12 deficiency without a clear dietary cause
- Deficiency that comes back when supplementation is stopped
- Macrocytic anaemia, glossitis or compatible neurological symptoms
- Hashimoto's thyroiditis, vitiligo, type 1 diabetes or another autoimmune condition together with suspected deficiency
- A personal or family history of autoimmune gastritis or pernicious anaemia
Clinical comment
The two antibodies do not mean the same thing. Intrinsic factor antibodies are highly specific: a positive result strongly supports pernicious anaemia. However, they are not present in every case, so a negative result does not exclude it.
Parietal cell antibodies are more sensitive but less specific. They can appear in other autoimmune conditions and in people without a clinically relevant deficiency. That is why they should not be used on their own to diagnose autoimmune gastritis.
NICE proposes these antibodies in steps, starting with intrinsic factor antibodies and extending the assessment if suspicion persists. We have included both in the same sample to offer a combined assessment when there is already a reasonable suspicion of an autoimmune cause. Bear in mind that, if the antibodies do not clarify the case, other tests may be required to complete the assessment.
Dr. Antonio Mas
What is tested
- Vitamin B12
- Measures the circulating concentration of cobalamin.
- Folic acid (folate)
- Detects folate deficiency, which can cause similar changes in the blood.
- Full blood count
- Looks for anaemia, enlarged red blood cells and other changes related to the deficiency.
- Homocysteine
- Can rise when B12 or folic acid is lacking and adds functional context, although it is not specific.
- Gastric parietal cell antibodies
- Relatively sensitive for autoimmune gastritis, but they can also appear in people without pernicious anaemia.
- Intrinsic factor antibodies
- Highly specific for pernicious anaemia when positive, although a negative result does not allow it to be excluded.
How to prepare
Fast for 8 to 12 hours. You can drink water. If you take vitamin B12 supplements or injections, say so before the sample is taken. Supplementation can change the B12 figure, although it does not affect the antibodies. Do not stop a prescribed treatment without discussing it first.
You can add
Without another needle. It is offered when you order, so you do not have to decide now.
- General blood testA general blood test with full blood count, glucose, cholesterol and kidney and liver function: the basic parameters included in any general check-up.+€59.00
- Coeliac disease antibodiesMeasures the antibodies used to investigate coeliac disease; for a reliable result, it must be done while you are still eating gluten.+€39.00
- Thyroid functionBrings together TSH and free T4, the two basic tests for assessing how the thyroid is working.+€29.00
Related blood tests
We have other profiles in Digestive with more or fewer tests:
- Lactose intolerance test€60.00
- Sorbitol intolerance test€60.00
- Fructose intolerance test€60.00
- SIBO breath test€64.00
- Helicobacter pylori breath test€69.00
- Coeliac disease blood test (antibodies)€69.00
- Vitamin B12 blood test€89.00
- Methylmalonic acid, for borderline B12 deficiency€149.00
- Coeliac disease genetic test (HLA DQ2/DQ8)€229.00
- Gut microbiota test€359.00
The most comprehensive is not always the most useful. Each profile page explains when it makes sense and when it does not.
What it is based on
National Institute for Health and Care Excellence (NICE)
Vitamin B12 deficiency in over 16s: diagnosis and management (NG239)
Recommends intrinsic factor antibodies when autoimmune gastritis is suspected as the cause of the deficiency, and places gastric parietal cell antibodies as the next step if the first test is negative and suspicion remains.
Devalia V, Hamilton MS, Molloy AM · British Journal of Haematology 166(4):496-513
Guidelines for the diagnosis and treatment of cobalamin and folate disorders
Recommends requesting intrinsic factor antibodies for anyone with anaemia, neuropathy or glossitis in whom pernicious anaemia is suspected, whatever the B12 figure, and warns that a negative result does not allow it to be excluded.
Protocol designed by Dr. Antonio Mas, specialist in Endocrinology and Nutrition, Spanish medical licence no. 080846289, and reviewed in September 2026.
This blood test is a standardised protocol and does not replace a medical consultation. If you have symptoms, a known condition or a complex clinical situation, speak to your doctor.