What does an intrinsic factor antibody test show?
Positive strongly suggests pernicious anaemia. Negative doesn’t rule it out. One NHS lab says the test finds only 40 to 75% of people who have it. So a negative can still need more tests.
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What does an intrinsic factor antibody test show?
It looks for antibodies against intrinsic factor. Antibodies are proteins your immune system makes. These ones target a protein you need to absorb B12.
A positive result strongly suggests the stomach condition behind pernicious anaemia. NICE calls it autoimmune gastritis.
A negative result does not rule it out. One NHS lab says the test finds only 40 to 75% of people who have it.
| Result | What it suggests | What usually happens next |
|---|---|---|
| Positive | Strongly suggests pernicious anaemia. | NICE advises lifelong B12 injections. |
| Negative | Does not rule it out. | More tests may follow if it’s still suspected. |
| Hard to read | Labs report results in different ways. | Your GP follows your lab’s guidance. |
Sources: NICE NG239; NICE rationale
Ask your GP which result you had, and what your lab says it means.
What is intrinsic factor, and who gets tested?
Intrinsic factor is a protein made by cells in your stomach. Think of it as a ticket B12 from food needs to get into your body. In pernicious anaemia, your immune system attacks the cells that make the tickets.
So this cause is not related to your diet, the NHS says.
How B12 gets in, and where pernicious anaemia blocks it
- 1
Food
B12 comes from meat, fish, milk and eggs.
- 2
Stomach
B12 joins intrinsic factor, made by stomach cells.
- 3
Gut
The pair is absorbed in the lower small gut (distal ileum).
- 4
The block
In pernicious anaemia, the immune system attacks the cells that make intrinsic factor.
Sources: NHS; NHS treatment
NICE says to consider the test if you have low B12 and your doctor suspects this cause. You don’t need it if you’ve tested positive before, or had surgery that affects B12 absorption, like removing your whole stomach.
Pernicious anaemia is more common in women around 60 and in people with a family history. It’s also more common if you have another condition where the immune system attacks the body, like Addison’s disease or vitiligo.
No B12 test yet? Start with the B12 blood test.
What does a positive intrinsic factor antibody mean?
It strongly suggests your low B12 comes from your stomach, not your diet. NICE advises lifelong B12 injections into a muscle.
Another UK lab says about 95 in 100 people who test positive do have pernicious anaemia.
What usually happens after a positive result
- 1
Injections start
At first, an injection every other day.
- 2
Then for life
Usually one every 2 to 3 months. If your nerves were affected, you’ll see a blood specialist (haematologist) and may need one every 2 months.
- 3
Symptoms ease
They could start to improve within 2 weeks, but this may take up to 3 months.
- 4
Ongoing checks
Tell your GP about new or worse indigestion, nausea or vomiting.
Sources: NHS; NICE NG239
Why the last step? NICE says people with this condition are at higher risk of a type of stomach tumour, and may be at higher risk of stomach cancer. New gut symptoms may mean a camera test (endoscopy).
Never stop or change a prescribed medicine without your prescriber. For how the jabs work, see B12 injections.
What if my intrinsic factor antibody test is negative?
You may still have pernicious anaemia. NICE says a negative result is less reliable and can’t rule it out.
Picture a smoke alarm that goes off in only some fires. When it sounds, there’s very likely a fire. When it’s quiet, you still can’t be sure there isn’t one.
That gap is why NICE lists four more tests, if your doctor still suspects it.
| Test | What it checks |
|---|---|
| Parietal cell antibodies | Antibodies against the stomach cells that make intrinsic factor. |
| Gastrin | Measures gastrin, a hormone your stomach makes to control stomach acid. |
| CobaSorb | Whether your body can absorb B12. |
| Gastroscopy with biopsy | A camera looks inside your stomach and takes a tiny sample. A specialist does it. |
Source: NICE NG239
NICE says only the camera test with a sample would normally settle it. None of the others can fully rule it out.
Still no cause after that? NICE says to offer a coeliac blood test, so ask your GP if you’ve had one.
What is a normal intrinsic factor antibody level?
There isn’t one UK number. Each lab sets its own cut-off, and NICE says labs should explain how to read their test.
| Lab | Normal (negative) result |
|---|---|
| Liverpool University Hospitals | Below 20 U/ml |
| Exeter Clinical Laboratory | 10.0 U/ml or below |
Sources: Liverpool lab; Exeter lab
So a 15 could be negative at one lab and positive at another. Check your number against the cut-off on your own report.
What to do with your antibody result
- Ask your GP what your lab says your result means.
- Tell your GP about any B12 tablets, injections or patches you already use.
- If you can, have blood taken for tests before you start B12 treatment.
- If your test was negative and your symptoms carry on, ask whether more tests are worth it.
- If you’re pregnant or breastfeeding and pernicious anaemia is suspected, ask about starting B12 injections without waiting for the result.
- If you have pernicious anaemia, or it’s suspected, tell your GP about new or worse indigestion, nausea or vomiting.
Source: NICE NG239
For the wider picture, see low B12 symptoms and anaemia blood tests.
When to speak to a GP
The NHS says some problems from low B12 can be permanent if left untreated. Book an appointment if:
- You have signs of low B12, such as feeling weak or tired, a sore or red tongue, pins and needles, numbness, balance problems or memory problems. See a GP.
- Your B12 is low, your antibody test was negative, and your doctor still suspects pernicious anaemia. Ask about the further tests NICE lists.
- You’re on B12 treatment and your symptoms haven’t improved, get worse or come back, or you get new ones. NICE says to seek help without waiting for your next appointment.
- You have pernicious anaemia, or it’s suspected, and you get new or worse indigestion, nausea or vomiting. NICE says to consider a camera test.
- You’re pregnant or breastfeeding and your B12 is low. NICE says injections start without waiting for the antibody result, if pernicious anaemia is suspected.
Tests for pernicious anaemia are not always conclusive, the NHS says. Your symptoms count too, so tell your GP about all of them.