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Pernicious anaemia: why your body cannot absorb B12 | CION Cancer Clinics
Pernicious anaemia is an immune condition that stops your stomach absorbing vitamin B12, however much you eat. The immune system damages the stomach cells that make intrinsic factor, the protein B12 needs to get into the blood. It causes tiredness, pale skin, a sore tongue and tingling nerves. B12 replacement that bypasses the stomach, usually injections, treats it, and most people need it lifelong. At CION Cancer Clinics, our haematologist cares for anaemia, bleeding, clotting and inherited blood disorders, with ArogyaSri, CGHS and cashless insurance accepted.
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Medically reviewed by Dr. Basudev PokhrelConsultant Haematologist · last reviewed September 2026, next review due September 2027
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On this page
- What is pernicious anaemia?
- Where does B12 absorption break down?
- What symptoms does pernicious anaemia cause?
- Which tests point to it, and what do the words mean?
- How is it treated, and does treatment stop?
- What do families often get wrong about it?
- What else should you watch for, and what can this page not tell you?
- Common questions about pernicious anaemia
The short answer
What is pernicious anaemia?
Pernicious anaemia is a long-term condition where your immune system stops your stomach from absorbing vitamin B12. You can eat plenty of B12 and still run short, because the vitamin never gets from your gut into your blood.
Why the stomach matters
B12 cannot cross the gut wall on its own. Cells in the stomach lining make a protein called intrinsic factor, which grips the B12 and carries it to the end of the small bowel, where it is taken in. In pernicious anaemia, the immune system attacks those stomach cells or the protein itself. Without intrinsic factor, most of the B12 in your food passes straight through.
How it differs from other B12 shortages
In India, the most common reason for low B12 is a diet with little or no milk, curd, eggs, fish or meat. That kind of shortage often improves when B12 is added back. Pernicious anaemia is different. The problem is absorption, so extra B12 in food does not fix it, and it does not go away over time.
Who tends to get it
It is more common in older adults and in women. It runs in some families. People who already have another condition where the immune system attacks the body, such as thyroid disease, type 1 diabetes or vitiligo, are more likely to develop it.
The old name "pernicious" means deadly. Before B12 was discovered, it was. Today it is a manageable, lifelong condition.How B12 gets in
Where does B12 absorption break down?
B12 is freed from food
Stomach acid loosens B12 from the protein in milk, eggs, fish and meat.
Intrinsic factor grips it
Cells in the stomach lining release intrinsic factor, which binds to the freed B12. This is the step pernicious anaemia breaks. The immune system damages those cells, or makes antibodies that block the protein.
The small bowel takes it in
The B12 and its carrier travel to the last part of the small bowel, where they are absorbed into the blood.
The liver stores it
The liver keeps a large store of B12. This is why symptoms creep in slowly. The store runs down quietly for a long time before your blood count or nerves show any sign.
Not sure whether this applies to you?
Ask an oncologistWhat you may notice
What symptoms does pernicious anaemia cause?
Symptoms build slowly, so many people put them down to age, stress or overwork. Not everyone gets all of them.
From a low blood count
Without B12, the bone marrow makes fewer red cells, and the ones it makes are too large. Your haemoglobin falls.
- Tiredness that sleep does not fix
- Breathlessness on stairs
- Pale or slightly yellow skin
- A racing or thumping heart
From the nerves
B12 keeps the protective coating of nerves healthy. Nerve symptoms can appear even when the haemoglobin is still normal.
- Pins and needles in the feet or hands
- Unsteady walking, especially in the dark
- Numbness that slowly spreads upwards
In the mouth and gut
Cells that renew quickly are affected early. A smooth, sore, red tongue is a classic sign. Mouth ulcers, loss of appetite and weight loss can also happen.
In memory and mood
Forgetfulness, low mood, irritability and poor concentration are common. In older parents, this is easily mistaken for ageing.
Nerve damage left untreated for a long time may not fully recover. Do not wait for it to pass.On your report
Which tests point to it, and what do the words mean?
- Serum B12
- The amount of B12 in your blood. A low value shows a shortage but not its cause. Reference ranges differ between laboratories.
- MCV (mean cell volume)
- The average size of your red cells. A high MCV means the cells are larger than usual, which fits B12 or folate shortage but has other causes.
- Intrinsic factor antibody
- A blood test for antibodies that block intrinsic factor. A positive result strongly suggests pernicious anaemia. A negative one does not rule it out.
- Parietal cell antibody
- Antibodies against the stomach cells that make intrinsic factor. Often positive, but also found in some healthy people, so it is read with care.
- MMA and homocysteine
- Two substances that build up when the body is short of B12. They help when the B12 result is borderline.
- Peripheral smear
- Your blood looked at under a microscope. Large red cells and white cells with extra lobes point towards B12 or folate shortage.
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Treatment
How is it treated, and does treatment stop?
Treatment replaces B12 in a way that does not rely on the stomach. For most people this means B12 injections, usually lifelong, because the absorption problem does not heal. Your doctor sets how often, and the schedule usually starts more often and then settles.
What to expect once it starts
Many people feel more energetic within the first weeks. The blood count recovers over the following months. Nerve symptoms improve more slowly, and some may not fully settle if they had been present for a long time. Your haematologist will repeat the blood count to check the response.
Tablets instead of injections
Some people are offered high-strength B12 tablets. A small part of a large amount of B12 can be absorbed without intrinsic factor. This does not suit everyone, especially people with nerve symptoms or poor follow-up. Do not switch from injections to tablets on your own. Discuss it with your treating team.
Why folic acid alone is not enough
Folic acid can lift the blood count while B12 stays low. The nerves can keep getting worse behind a better report. This is why both B12 and folate are checked before treatment.
Commonly believed
What do families often get wrong about it?
"Eating more curd and eggs will fix it."
Diet helps a shortage caused by diet. In pernicious anaemia the stomach cannot absorb B12, so more B12 in food does not reach the blood. Replacement that bypasses the stomach is needed.
"The report is normal now, so the injections can stop."
The report is normal because of the injections. The cause is still there. Stopping lets the store run down again, and nerve damage can return without warning signs in the blood count first.
"A low blood count with big red cells means blood cancer."
B12 shortage is a far more common reason for large red cells than any marrow disease. It can even make the marrow look unusual under the microscope. Your haematologist checks B12 and folate before thinking about rarer causes.
"Tingling feet in an older parent is just age."
It may be age, diabetes or something else. It may also be B12 shortage, which is treatable. A simple blood test is worth doing before accepting it as normal.
Being straight with you
What else should you watch for, and what can this page not tell you?
Once treated, most people with pernicious anaemia live a normal life. Two things need attention over the years.
Your stomach
Long-term immune damage to the stomach lining slightly raises the chance of some stomach growths, including stomach cancer. Your doctor may suggest an endoscopy, a camera test of the stomach, particularly if you have indigestion, vomiting, weight loss or black stools. Report these rather than waiting.
Other immune conditions
Thyroid problems often travel with pernicious anaemia. A thyroid blood test from time to time is reasonable.
What this page cannot tell you
It cannot tell you whether your own low B12 is pernicious anaemia, diet, medicines or a gut problem. That needs your full reports, examination and sometimes repeat tests. A single B12 value is read alongside symptoms and the blood count. CION's haematology team reviews the whole picture and tells you which test, if any, should come next.
Questions we are asked
Common questions about pernicious anaemia
Is pernicious anaemia a type of cancer?
No. It is an immune condition that stops your stomach absorbing B12. It is not cancer and does not turn into leukaemia. It does slightly raise the chance of some stomach problems over many years, which is why your doctor may ask about indigestion or suggest a stomach check.
Will I need B12 injections for the rest of my life?
Usually, yes. The stomach damage does not heal, so the body keeps needing B12 from a route that bypasses it. Some people are later moved to high-strength tablets under close follow-up. That decision belongs to your treating doctor, not to a good blood report.
Is it hereditary? Should my children be tested?
It does run in some families, but most children of an affected parent never develop it. There is no routine screening for healthy relatives. If a family member develops tiredness, tingling or a sore tongue, mention the family history to their doctor and ask for a B12 test.
My B12 is low but the antibody test is negative. What now?
A negative intrinsic factor antibody does not rule out pernicious anaemia, because the test misses a good share of people who have it. Your doctor looks at your diet, medicines, gut history and response to treatment. Sometimes the cause stays uncertain and treatment continues anyway.
Can I eat normally with pernicious anaemia?
Yes. There is nothing you need to avoid. A balanced diet is good for your general health, but it will not replace your treatment, because the B12 in food cannot be absorbed properly. Vegetarian and non-vegetarian families both need the same replacement if the diagnosis is confirmed.
Why do my feet still tingle after starting treatment?
Nerves recover far more slowly than blood cells. Improvement can continue over many months. If tingling was present for a long time before diagnosis, some may remain. Tell your doctor if it worsens, because diabetes, thyroid problems or other causes may also be playing a part.
Can I have B12 injections during pregnancy?
B12 replacement is generally continued in pregnancy, because the baby also depends on your B12. Tell your obstetrician and haematologist as soon as you know you are pregnant. They will check your B12 and folate and plan your care together.
Which doctor should I see for pernicious anaemia?
A general physician often starts the tests. A haematologist, a blood specialist, helps when the count is very low, the cause is unclear, or the blood cells look unusual. A gastroenterologist may be involved for stomach checks. Bring every earlier blood report to the first visit.
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Sources
- NHS — Vitamin B12 or folate deficiency
- NIH Office of Dietary Supplements — Vitamin B12 fact sheet for consumers
- NICE — B12 and folate deficiency (Clinical Knowledge Summary)
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
B12 Deficiency ExplainedThe wider picture of low B12 and its symptomsReading a B12 Result and Borderline ValuesWhat your B12 number does and does not meanB12 Injections vs TabletsWho each route suitsHow Long B12 Treatment ContinuesWhy some people need treatment for lifeNerve Symptoms From B12 DeficiencyTingling, numbness and how nerves recover
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