Iron Deficiency Anaemia (IDA)
NICE CKS Anaemia – iron deficiency. Last revised: Oct 2025.
Epidemiology
Iron deficiency is the most common cause of anaemia. [Ref]
Aetiology
Causes / risk factors of anaemia can be categorised as following: [Ref]
| Physiological (↑ demand) |
|
| Blood loss | Chronic blood loss from:
|
| Malabsorption |
|
It is worth noting that dietary deficiency (e.g. from vegetarian and vegan diets) is rarely a cause of IDA on its own in adults. It takes about 8 years for a healthy adult male to develop iron deficiency anaemia due to a poor diet or malabsorption resulting in no iron intake.
In contrast, dietary insufficiency is the main contributor to IDA in infancy. Prolonged exclusive breastfeeding (after 6 m/o) without introduction of iron-rich complementary food is associated with increased risk, as iron requirements increase rapidly after 6 m/o and breast milk alone does NOT provide sufficient iron to meet these needs. [Ref]
Clinical Features
| Non-specific anaemia features | Symptoms:
Signs:
|
| Features specific to IDA |
|
Plummer-Vinson syndrome is a rare manifestation of IDA, but is an exam-classic. It is characterised by a triad of: [Ref]
- IDA
- Dysphagia
- Oesophageal webs
It occurs predominantly in middle-aged women.
Investigation and Diagnosis
Diagnosing IDA
Key laboratory findings in IDA:
| Investigation category | Findings in IDA |
|---|---|
| FBC | Microcytic, hypochromic anaemia
↓ / normal reticulocyte count:
|
| Iron studies |
|
| Peripheral blood smear |
|
Serum ferritin level most reliably correlates with relative total body iron stores. In all people, a serum ferritin level of <30 micrograms/L confirms a diagnosis of iron deficiency.
However, ferritin level can be difficult to interpret in the presence of concurrent infection or inflammation, as ferritin level are increased independently of iron status (ferritin is an acute phase reactant). In these patients, ferritin level can be normal or high in the presence of iron deficiency.
It is common to confuse anaemia of chronic disease with iron deficiency anaemia, as both can cause microcytic / normocytic anaemia.
| Test | Iron deficiency anaemia | Anaemia of chronic disease |
|---|---|---|
| Serum iron | ↓ | ↓ |
| Ferritin | ↓ | ↑ (or normal) |
| TIBC | ↑ | ↓ |
| Transferrin | ↑ | ↓ |
| Transferrin saturation | ↓ | ↓ |
Note that ferritin can be normal or ↑ in iron deficiency anaemia, if there are concurrent infection / inflammation. In such cases, interpreting the TIBC, transferrin, and transferrin saturation becomes important.
Investigating Underlying Cause
Tests for ALL patients with IDA:
- Coeliac serology (to screen for coeliac disease – see the Coeliac Disease article for more information)
- Urinalysis (to test for haematuria)
- FIT test (in adults – to guide referral of suspected colorectal cancer – see the Colorectal Cancer article for more information)
Consider stool examination (to detect parasitise), if appropriate from the person’s travel history
NICE CKS commented that it is usually unnecessary to further investigate the following patients prior to treatment:
- Otherwise healthy young people in whom history clearly suggests a cause (e.g. regular blood donors)
- Menstruating young women with no history of GI symptoms or family history of colorectal cancer
- Pregnant women (further investigations are only necessary if the anaemia is severe / no response to iron supplementation / history and examination suggest an alternative cause of IDA)
Red Flags
In adults, anaemia may be a presenting feature of colorectal cancer. NICE outlined the following as red flags for colorectal cancer that warrant further investigations:
- Adults with iron deficiency anaemia
- >60 y/o AND anaemia (any type, even in the absence of iron deficiency)
These patients should be offered a test to guide subsequent referral. See the Colorectal Cancer article for more details (NB that there are other non-anaemia related red flags for colorectal cancer).
Management
Address any underlying causes, some examples include:
- Treat heavy menstrual bleeding (see the Heavy Menstrual Bleeding (HMB) article for more information)
- Optimise dietary factors, if thought to be a contributor cause
- Maintain adequate balanced diet of iron-rich foods (e.g. dark green vegetables, iron-fortified breast, meat, apricots, prunes, raisins)
- Consider referral to dietitian
Offer all patients treatment with iron supplementation
- 1st line: oral ferrous sulfate / fumarate / gluconate
- 2nd line: parenteral iron
- Do not wait for investigations to be carried out before prescribing iron supplements
It is important to note that treatment should be continued for another 3 months, after IDA has been corrected (i.e. haemoglobin and red cell indices are back to normal), before stopping treatment (to aid replenishment of iron stores).
Key Prescribing Information
Instructions:
- Ideally to be taken on an empty stomach to maximise absorption
- If iron is taken with or after food, absorption is affected but also reduces adverse effects
Important adverse effects to advise patients on:
- Constipation
- Stool discolouration (e.g. black stools – may mimic melena)
- GI upset (e.g. nausea, diarrhoea, abdominal pain)
If the patient finds the adverse effects troublesome and affects compliance:
- Offer a laxative to people with constipation
- Recommend the person takes iron with or after meals
- Consider alternative oal preparation
- Reduce the dose frequency of the iron supplement to alternate days
Key interactions with iron supplementations:
| Iron reduces the absorption / effects of some drugs if taken together |
|
| Absorption of iron is reduced if taken concurrently with |
*In contrast, vitamin C improves the absorption of iron |
Follow-Up and Monitoring
Re-check FBC, to assess haemoglobin levels within the first month of treatment
- Expected response: haemoglobin concentration should increased by ~20 g/L over 3-4 weeks
- If there is an inadequate response → assess compliance (if compliance is not an issue → refer for specialist assessment)