Reasoning GP · Algorithm · 1-page summary
Anaemia (low Hb) in adults
For: adults with a low Hb result or suspected anaemia, including the results inbox. Not for: children (use paediatric guidance). Pregnancy and postpartum go straight to block 2 (maternity).
Core rule: anaemia is Hb <130 g/L in men, <120 g/L in non-pregnant women (use local ranges). Iron deficiency is a finding, not a diagnosis: ask where the blood is going before prescribing iron. Take ferritin, B12 and folate before treating or transfusing whenever clinically safe.
0Stop — emergency now — at any Hb, on seeing the result
- Compromise: collapse, shock, major haemorrhage, severe symptomatic anaemia, severe hypoxia, altered consciousness, heart failure → 999. Chest pain with ECG changes → 999, manage as ACS whatever the Hb.
- Active bleeding: haematemesis, melaena, large rectal bleed, heavy menstrual loss with postural symptoms; ongoing postpartum haemorrhage → 999
- Before handover: obs with postural BP; ferritin, B12, folate before transfusion if safe. Stop NSAIDs; discuss anticoagulation with the receiving team. Send FBC (all lines, film), previous values, drugs. Transfusion follows symptoms and bleeding, not Hb alone.
1Triage by MCV — with ferritin, CRP and other cell lines
| MCV fL | Think |
|---|---|
| <80 | Iron deficiency until proved otherwise, or thalassaemia trait |
| 80–100 | Acute bleed, chronic disease, CKD, myeloma, haemolysis, mixed |
| >100 | B12/folate, alcohol, liver, thyroid, drugs, myelodysplasia |
| Other line | Abnormal WCC, platelets or film = marrow, not iron → block 2 |
2Screen — one row is enough
- Hb <70 g/L with symptoms or a rapid fall → Same-day hospital
- Abnormal second cell line, or fever, bruising, petechiae, bone pain → Same-day haematology; blasts or neutropenic fever → admit now. No iron, B12 or folate meanwhile.
- Haemolysis (jaundice, dark urine) → urgent; fast fall, haemoglobinuria, renal impairment → Same-day haematology. Stop the suspected drug.
- B12 with neurology (paraesthesiae, gait, cognition; nitrous oxide?) → Same-day: bloods, then treat.
- Pregnancy: Hb <110 g/L (1st trimester), <105 (later) → start oral iron and inform the midwife; Hb <70 g/L, significant symptoms, rapid fall or late gestation (>34 weeks) → Same-day maternity; bleeding or compromise → 999
- NG12: IDA any age, or anaemia at 60+ → FIT; ≥10 µg Hb/g → Urgent cancer. Dysphagia, or 55+ with weight loss plus upper abdominal pain, reflux or dyspepsia → Urgent upper GI. Rectal or anal mass or anal ulcer → refer without FIT.
3Assess — whole panel before treatment
☐ Postural BP, pallor, jaundice, nodes, spleen, abdomen, bruising; PR if indicated; neurology if B12 possible; menstrual history ☐ FBC, ferritin + CRP, U&E/eGFR, LFTs, TFTs, coeliac serology (tTG-IgA + total IgA); B12 + folate if macrocytic or neurology; film, reticulocytes, haemolysis screen if indicated; protein electrophoresis + free light chains at 60+
4Classify — only if the screen is negative
- Iron deficiency — ferritin <30 µg/L (≤100 with TSAT <20% in inflammation). Men, postmenopausal women → upper and lower GI investigation unless a clear other cause. Premenopausal → quantify periods; GI if 50+, GI symptoms or CRC family history (BSG), recurrent or poor response; coeliac serology for all.
- Thalassaemia trait — low MCV, normal ferritin, normal/high red cell count → haemoglobinopathy screen, not iron.
- Chronic disease / CKD — exclude deficiency and myeloma first; eGFR >60: find another cause.
- Marrow — unexplained, persistent or progressive macrocytosis; other cytopenias; renal impairment, bone pain, raised ESR (myeloma) → haematology.
- B12 / folate — send both; B12 <180 ng/L deficient, 180–350 indeterminate.
- Uncertain — no source, or no Hb rise in 2–4 weeks of iron: say so → block 6; name the reviewer.
5Treat today — stable, panel sent
- Iron: one oral iron once daily (about 50–100 mg elemental; ferrous sulfate 200 mg ≈ 65 mg); alternate days if not tolerated. Alongside FIT and GI referral, never instead. Continue 3 months after Hb normalises.
- B12: hydroxocobalamin IM; neurology → 1 mg alternate days until no further gain, then 2-monthly. Never folate alone before B12.
- Heavy periods: treat the loss too (NG88). Doses: SPC and local formulary.
6Refer routinely
- IDA with no source, no response or recurrent → gastroenterology. Oral iron unsuitable → local IV iron pathway (MHRA: hypophosphataemia with ferric carboxymaltose).
- Coeliac → gastroenterology (no gluten-free diet first). Haemoglobinopathy → haematology. CKD needing ESA → renal.
7Never reassure by
- A normal MCV, or a normal ferritin in inflammation, CKD, liver disease or cancer.
- A FIT <10 µg Hb/g with persistent symptoms, recurrent IDA, a mass or real concern.
- A normal colonoscopy with the upper GI tract unexamined.
- "Menorrhagia" without quantifying loss or checking coeliac; "dietary" over 50.
- "Chronic disease" without excluding deficiency and myeloma.
- Filing an Hb alone without the MCV, white count, platelets and film.
8Safety-net — say it, then document it
999 “Call 999 if you collapse or feel faint, your heart races, you vomit blood or pass black tarry stools, or have chest pain with breathlessness.” Same day: “Contact us or 111 today for bloody stools, heavy bleeding, worse breathlessness at rest, new palpitations, ankle swelling, or new numbness, weakness or clumsiness.” Recheck FBC at 2–4 weeks with written thresholds.
Results inbox / remote: convert to face to face or emergency for compromise, active bleeding, an abnormal second cell line, neurology with macrocytosis, pregnancy or a rapid fall. Hb <70 or blasts never sit in an inbox overnight.
✓Safe to manage in primary care only if — all five, documented
No block 0–2 row applies; obs normal, no postural drop
White count, platelets (and film) normal
Full panel sent before treatment; MCV and ferritin read with CRP
FIT <10, no NG12 criterion; clear non-sinister cause treated
Recheck at 4 weeks, named reviewer; safety-net given
Summary of the full Reasoning GP anaemia algorithm, which holds the detail, examination, ongoing management and evidence. Sources: NICE NG12 (updated April 2026), NG203, NG239, NG88, NG20; BSG 2021 iron deficiency anaemia; BSH 2020 iron deficiency in pregnancy; ACPGBI/BSG 2022 FIT; WHO Hb thresholds; MHRA. Clinical reference — follow local acute-transfer, haematology and prescribing policies and check doses in the SPC and your local formulary.