Reasoning GP · Algorithm · 1-page summary

Low ferritin in adults

For: adults with a low ferritin (iron deficiency with or without anaemia) in primary care. Not for: children; a raised ferritin (use the high ferritin algorithm). Pregnancy: block 1.

Reviewed October 2026 · next review April 2027

BSG IDA 2021NICE NG12 / HTG690NICE NG20NICE NG88BSH pregnancy 2020

Core rule: unexplained iron deficiency in a man of any age or a post-menopausal woman is GI blood loss until proved otherwise. Do not assume diet; arrange gastroscopy and colonoscopy. A negative FIT does not exclude GI pathology.

0Stop — act today — before anything else

Active significant GI bleeding with haemodynamic instability → 999
Severe symptomatic anaemia (dyspnoea at rest, chest pain, syncope, heart failure symptoms) or rapidly falling Hb → Same-day hospital assessment; transfusion decided on symptoms, not Hb alone.
New visible rectal bleeding, melaena or haematemesis at any point → Same-day assessment (999 if collapse or haemodynamic instability).
Pregnancy with severe or rapidly worsening anaemia → Same-day maternity team.

1Triage — who is the patient?

Group	Action
Man (any age), post-menopausal woman	Unexplained IDA → bidirectional GI investigation (block 2) unless risks clearly outweigh benefits.
Pre-menopausal woman	Clear heavy menstrual bleeding (HMB), no red flags → iron + treat HMB (NG88). Investigate GI if GI symptoms, CRC family history, or IDA disproportionate, recurrent or refractory.
No anaemia	Lower GI risk; still keep a low threshold to investigate the groups above.
Pregnancy	Oral iron first line. Discuss significant or rapidly worsening IDA promptly with maternity; consider IV iron, generally from the 2nd trimester.
Inflammation, CKD	Acute-phase reactant: normal ferritin does not exclude deficiency → CRP + TSAT.

2Screen — serious causes

Rectal bleeding, melaena, weight loss or change in bowel habit → FIT per NG12/HTG690; FIT ≥10 µg Hb/g → suspected cancer pathway. Negative or unavailable FIT: do not delay referral if concern is significant.
Rectal mass, unexplained anal mass or anal ulceration → consider suspected cancer pathway without waiting for FIT.
Unexplained IDA, man or post-menopausal woman → gastroscopy + colonoscopy (CT colonography if unsuitable), Urgent pathway. New GI symptoms on treatment → OGD or colonoscopy.
Unexplained visible haematuria aged ≥45 or haemoptysis aged ≥40 → suspected cancer pathway (NG12); investigate each source.

3Assess

☐ Menstrual, GI, diet, pregnancy, family history (CRC, coeliac) ☐ NSAIDs, aspirin, anticoagulants, PPIs ☐ Examination incl. rectal (melaena, mass) ☐ FBC (a normal MCV does not exclude), ferritin; CRP + transferrin saturation if inflammation possible ☐ Urinalysis ☐ Anti-tTG IgA + total IgA while eating gluten ☐ FIT per pathway

Targeted: renal function, B12/folate, Hb electrophoresis (thalassaemia?); H. pylori test after non-explanatory GI evaluation or with dyspepsia.

4Classify — find the source

GI loss — most important cause in men and post-menopausal women; haemorrhoids only by exclusion → block 2.
Menstrual loss — commonest in pre-menopausal women → treat HMB per NG88.
Malabsorption — coeliac (most important), H. pylori, IBD, gastric/bariatric surgery, PPI → serology / gastroenterology.
Demand or diet — pregnancy, breastfeeding, endurance athletes, vegan/vegetarian; diet alone rarely causes severe IDA in the UK.
Not iron deficiency — thalassaemia trait (ferritin normal/high, Mentzer index <13) → Hb electrophoresis.
Uncertain — IDA without clear explanation after basic tests → gastroenterology.

5Treat today — doses: NICE/SPC, BNF, local formulary

Oral iron: one tablet once daily (e.g. ferrous sulphate 200 mg); not tolerated → alternate days, another preparation or IV iron. Vitamin C not routinely needed.
IV iron (local protocol, product-specific dose): oral failed or not tolerated, malabsorption, ongoing loss, rapid correction, CKD. Ferric carboxymaltose → hypophosphataemia risk (MHRA).
Treat the cause: HMB per NG88; stop NSAIDs where possible; review PPI need; H. pylori → eradicate per formulary; coeliac → gluten-free diet via coeliac pathway.
Diet: iron-rich foods; tea, coffee, calcium reduce absorption.

6Refer routinely — and follow up

Recheck Hb at ~2–4 weeks (rise ≥10 g/L within 2 weeks supports response); continue iron ~3 months after Hb normalises.
No Hb rise at 4 weeks: check adherence, coeliac, ongoing loss, mixed deficiency, diagnosis → consider IV iron; haematology if no cause found.
Recurrent or refractory IDA after adequate bidirectional endoscopy → gastroenterology (small-bowel assessment); consider renal tract.
Gynaecology: HMB with recurrent IDA despite NG88 treatment, or structural cause.

7Never reassure by

"It's dietary" in a man or post-menopausal woman.
A negative FIT in confirmed IDA.
One normal endoscopy — upper and lower are both needed.
A normal MCV, or a normal ferritin in inflammation or CKD.
Haemorrhoids as the explanation.
A normal Hb after iron, without the cause found.

8Safety-net — say it, then document it

999 “Call 999 if you collapse, or are bleeding heavily and feel faint.” Same day “Contact us today if you have black tarry or bloody stools, vomit blood, or your breathlessness or chest pain gets worse. Iron tablets alone can make stools dark.” Book the Hb recheck with a date.

Result received remotely: rapidly falling Hb or severe symptoms → same-day assessment; new IDA in a man or post-menopausal woman → arrange GI investigation, do not file it as diet.

✓Safe to manage in primary care only if — all five, documented

No block 0 trigger; patient well Source sought for the patient's group (block 1) Coeliac serology + urinalysis done Iron started; Hb recheck dated at 2–4 weeks Referrals made; safety-net given

Summary of the full Reasoning GP low ferritin algorithm, which holds iron indices, thalassaemia, IV iron dosing, transfusion, pregnancy and evidence. Sources: BSG iron deficiency anaemia guideline (2021); BSH iron deficiency in pregnancy (2020); NICE NG12 (updated April 2026), HTG690, NG24, NG88, NG20; MHRA ferric carboxymaltose; local formulary. Clinical reference — follow local pathways and check doses: NICE/SPC, BNF.