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Health condition · Clinically reviewed

Anaemia, from a low haemoglobin to a clear cause and a working plan.

Not a diagnosis on its own - a signal that something else needs finding. Classify by red-cell size, replace what is missing and treat the underlying cause.

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Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against NICE, BSH and BSG sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK haematology practice including IV iron, B12 replacement and the 2-week wait pathway for iron deficiency.

Key facts

Anaemia at a glance.

The essentials, in plain English - what it is, how it is classified and how it is treated in the UK today.

  • What it is

    A reduction in haemoglobin below the normal range - under 130 g/L in men, 120 g/L in non-pregnant women and 110 g/L in pregnancy.

  • How it is classified

    By red-cell size (MCV) - microcytic (under 80 fL), normocytic (80 to 100 fL) or macrocytic (over 100 fL) - which points to the likely cause.

  • Most common cause

    Iron deficiency - usually from GI blood loss, heavy menstrual bleeding, poor dietary intake, malabsorption (coeliac) or pregnancy.

  • Macrocytic drivers

    B12 or folate deficiency, alcohol, hypothyroidism, liver disease and drugs like methotrexate or hydroxycarbamide.

  • Haemolysis

    Raised bilirubin, LDH and reticulocytes with low haptoglobin - hereditary (sickle cell, G6PD) or acquired (autoimmune, MAHA).

  • Foundation treatment

    Treat the underlying cause and replace the missing nutrient - iron, B12 or folate. Transfuse only when severe or symptomatic.

Why this guide matters

Classify first, replace second, investigate always.

Anaemia is a sign, not a diagnosis. The three points below shape everything else on this page.

  • The MCV points to the cause

    Microcytic (iron, thalassaemia), normocytic (chronic disease, CKD, acute loss) or macrocytic (B12, folate, alcohol, hypothyroidism, MDS).

  • Replacement is not the whole plan

    Iron, B12 or folate corrects the count - finding the source of blood loss or malabsorption stops it coming back.

  • Some pictures need urgent workup

    Iron deficiency in men, pancytopenia and haemolysis with fever or purpura are not for slow investigation.

How the diagnosis is made

From a low haemoglobin to a working diagnosis.

The steps a UK GP or haematologist will normally follow, in order - so you know what to expect and why.

  1. 01

    Assessing

    History and dietary review

    Diet, menstrual pattern, GI symptoms, family history, medications, travel and occupational exposure - each points to a different cause.

  2. 02

    Assessing

    Focused examination

    Pallor, koilonychia, glossitis, angular cheilitis, jaundice and splenomegaly - each sign narrows the differential.

  3. 03

    Assessing

    Full blood count and film

    FBC with MCV plus reticulocytes and a peripheral blood film - the film often shows the diagnosis before the bloods return.

  4. 04

    Confirming

    Cause-specific bloods

    Ferritin and iron studies, B12 and folate, TSH, LFTs, U&E and coeliac serology - guided by the MCV pattern.

  5. 05

    Confirming

    GI investigation if iron deficient

    Adults over 55 with unexplained iron deficiency need a 2-week wait upper and lower GI investigation to exclude malignancy.

  6. 06

    Specialist

    Haemolysis workup

    DAT (direct antiglobulin test), haemoglobin electrophoresis and G6PD screening when the film or bloods suggest haemolysis.

  7. 07

    Specialist

    Bone marrow biopsy (selective)

    Reserved for suspected MDS, leukaemia or persistent unexplained anaemia - always via haematology.

Typical timeline: a first visit to a clear cause in days to weeks, depending on the pattern.

Symptoms

What anaemia actually feels like.

The classic mix of fatigue, breathlessness and pallor - plus the signs that point at a specific cause and the features that mean it is time to escalate.

  • Fatigue and reduced exercise tolerance

    The commonest presentation - creeping tiredness and breathlessness on stairs that patients often blame on age or stress.

  • Pallor

    Best assessed in conjunctivae, palmar creases and nail beds - a specific but insensitive sign.

  • Palpitations and tachycardia

    The compensatory response to a lower oxygen-carrying capacity - worse on exertion.

  • Koilonychia and brittle nails

    Spoon-shaped nails and hair thinning - classic signs of long-standing iron deficiency.

  • Glossitis and angular cheilitis

    A smooth, sore tongue and cracked mouth corners - common with iron, B12 or folate deficiency.

  • Neurological features (B12)

    Peripheral paraesthesiae, gait instability and cognitive change - subacute combined degeneration if untreated.

  • Jaundice and dark urine

    Suggestive of haemolysis - raised unconjugated bilirubin with a low haptoglobin.

  • Red flag - chest pain or syncope

    Severe symptomatic anaemia (Hb under 70 g/L) needs same-day assessment and often transfusion.

Treatment

How anaemia is treated in the UK.

Replace what is missing, treat the underlying cause and refer or transfuse when the picture demands it.

  • Oral iron replacement

    Ferrous sulphate 200 mg once to three times daily with vitamin C for absorption - alternate-day dosing improves tolerance.

  • IV iron

    Ferric carboxymaltose or iron sucrose when oral iron is not tolerated, absorbed or fast enough - useful in IBD, CKD and late pregnancy.

  • B12 replacement

    IM hydroxocobalamin 1 mg three times weekly for two weeks then every three months for pernicious anaemia - high-dose oral for dietary deficiency.

  • Folate replacement

    Oral folic acid 5 mg daily - always check and replace B12 first to avoid unmasking neurological disease.

  • Menstrual management

    LNG-IUS, tranexamic acid or hormonal treatment for heavy menstrual bleeding - a common and often overlooked driver.

  • Erythropoiesis-stimulating agents

    EPO analogues for anaemia of chronic kidney disease and selected chemotherapy patients - specialist-led.

  • Red-cell transfusion

    Reserved for symptomatic, severe or acute anaemia - target the lowest Hb that relieves symptoms, not a set number.

  • Haematology referral

    For MDS, suspected leukaemia, haemolytic anaemia, haemoglobinopathy or persistent unexplained anaemia despite full workup.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and specialist society standards, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your GP or haematologist knows your history and can tell you which parts apply to you. If in doubt, get seen.

  • NICE. Anaemia - iron deficiency: clinical knowledge summary.

  • NICE. Anaemia - B12 and folate deficiency: clinical knowledge summary.

  • British Society for Haematology (BSH). Guidelines on iron deficiency, B12 and haemolytic anaemias.

  • British Society of Gastroenterology (BSG). Guidelines for the management of iron deficiency anaemia.

  • NICE NG12. Suspected cancer: recognition and referral - 2-week wait pathway for iron deficiency in adults.

Red flags

When anaemia needs urgent attention.

Most anaemia is manageable in primary care. These are the situations that are not - and where specialist or urgent input is needed.

  • Severe symptomatic anaemia

    Chest pain, syncope, breathlessness at rest or Hb under 70 g/L needs same-day assessment and often transfusion.

  • Iron deficiency in men or post-menopausal women

    Assume GI blood loss until proven otherwise - a 2-week wait upper and lower GI referral is standard.

  • Rectal bleeding or melaena

    Any overt GI blood loss with anaemia needs urgent investigation - do not wait for the ferritin.

  • B12 deficiency with neurological signs

    Paraesthesiae, gait ataxia or cognitive change - start IM hydroxocobalamin promptly to prevent permanent damage.

  • New pancytopenia

    Low haemoglobin with low white cells and platelets - urgent haematology referral for suspected marrow failure or leukaemia.

  • Haemolysis with fever or purpura

    Suspect TTP, HUS or DIC - a haematological emergency requiring immediate hospital assessment.

  • Sickle cell crisis

    Severe pain, chest symptoms or fever in a known sickle cell patient - urgent hospital pathway.

  • Anaemia in pregnancy

    Hb under 110 g/L in the first trimester or under 105 g/L later - treat early to protect mother and baby.

  • Persistent unexplained anaemia

    When bloods and standard workup are unrevealing - haematology referral for further investigation including marrow biopsy.

Living with it

A treatable condition, with a clear ladder.

Four things that make the biggest difference day to day - fixing the cause, taking iron the right way, keeping up B12 maintenance and rechecking the bloods.

A quiet reminder

The count rises long before the stores refill.

Keep taking iron for three months after the haemoglobin normalises - that is what stops the anaemia coming back.

  1. 01 Cause

    Treat the underlying cause

    Replacement alone is not enough - fixing the source of blood loss or malabsorption is what stops the anaemia coming back.

  2. 02 Iron

    Take iron the right way

    On an empty stomach with orange juice or vitamin C, away from tea, coffee and calcium - and give it three months to rebuild stores.

  3. 03 B12

    Do not skip maintenance

    Pernicious anaemia is lifelong - three-monthly injections protect the nervous system as well as the blood.

  4. 04 Follow-up

    Recheck the bloods

    Repeat FBC and ferritin at three months to confirm the response - and again if symptoms return.

Frequently asked

Everything we get asked about anaemia.

Quick answers on iron deficiency, B12 replacement, colonoscopy referral and when to transfuse.

  • What is anaemia?

    Anaemia is a reduction in haemoglobin below the normal range - under 130 g/L in men, 120 g/L in non-pregnant women and 110 g/L in pregnancy. It is a sign of an underlying problem, not a diagnosis in itself, and the pattern of red-cell size (MCV) points to the likely cause.

  • What causes iron deficiency anaemia?

    In the UK the commonest causes are heavy menstrual bleeding in pre-menopausal women and GI blood loss in men and post-menopausal women. Poor dietary intake, malabsorption (coeliac disease is a classic hidden cause) and pregnancy are the other major drivers.

  • How is iron deficiency treated?

    Oral ferrous sulphate 200 mg one to three times daily with vitamin C to help absorption - alternate-day dosing often works just as well with fewer side effects. IV iron (ferric carboxymaltose or iron sucrose) is used when oral iron is not tolerated, not absorbed or when correction needs to be quick.

  • When do I need a colonoscopy for anaemia?

    Adults over 55 with unexplained iron deficiency, or anyone with a positive faecal immunochemical test, warrant a 2-week wait upper and lower GI investigation to exclude a bowel cancer or coeliac disease.

  • What is pernicious anaemia?

    An autoimmune condition where antibodies against parietal cells or intrinsic factor stop the stomach absorbing B12. It causes a macrocytic anaemia and, if untreated, neurological damage. Treatment is lifelong IM hydroxocobalamin - three injections a week for two weeks, then every three months.

  • When is a blood transfusion needed?

    Transfusion is reserved for severe or symptomatic anaemia - typically Hb under 70 g/L, or under 80 g/L with cardiac disease. It buys time while the underlying cause is treated and is not a substitute for finding and fixing that cause.

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