What is anaemia and how is it managed?

Understanding and Managing Anaemia

Definition and Diagnosis

Anaemia is defined as haemoglobin <13 g/dL in men and <12 g/dL in women, representing a decreased circulating red blood cell mass that results from blood loss, destruction, or impaired production. 1

Key Diagnostic Thresholds

• Men: Hb <13 g/dL 1
• Non-pregnant women: Hb <12 g/dL 1
• Pregnant women: Hb <11 g/dL 1
• Use your laboratory's lower limit of normal range as the reference standard 1

Critical Investigation Triggers

• Men with Hb <12 g/dL require urgent investigation 1
• Postmenopausal women with Hb <10 g/dL require urgent investigation 1
• Any level of anaemia warrants investigation when iron deficiency is present 1

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Classification by Red Cell Size (MCV)

The diagnostic approach is algorithmically structured by mean corpuscular volume (MCV):

Microcytic Anaemia (MCV <80 fL) 1

Iron deficiency is the primary concern and requires:

• Serum ferritin <100 μg/L 1
• Transferrin saturation (TSAT) <20% 1, 2
• Reticulocyte haemoglobin equivalent (RetHe) <29 pg 1
• Percentage of hypochromic cells >10% 1

Critical pitfall: In patients of appropriate ethnic background (Mediterranean, Asian, African descent), perform haemoglobin electrophoresis to exclude thalassaemia before pursuing extensive GI investigations 1

Normocytic Anaemia (MCV 80-100 fL) 1

Evaluate for:

• Chronic kidney disease (check creatinine) 1
• Inflammatory/chronic disease (check CRP) 1
• Mixed deficiencies 1

Macrocytic Anaemia (MCV >100 fL) 1

Measure vitamin B12 and folate levels immediately 1:

• Folate deficiency: serum folate <10 nmol/L (4.4 μg/L) or RBC folate <305 nmol/L 1
• B12 deficiency: serum B12 <150 pmol/L 1
• If B12 borderline, measure methylmalonic acid (>271 nmol/L confirms deficiency) 1
• Check TSH for hypothyroidism 1

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Investigating the Underlying Cause

For Iron Deficiency Anaemia in Adults

All postmenopausal women and all men with confirmed IDA require both upper and lower GI investigation unless there is documented significant non-GI blood loss 1:

1. Screen for coeliac disease with tissue transglutaminase (tTG) antibody in all patients 1

   • If tTG negative, duodenal biopsies are unnecessary unless diarrhoea or other symptoms present 1
   • Pretest probability of coeliac disease in IDA alone is ~5% 1

2. Upper endoscopy (OGD) 1

   • Only advanced gastric cancer or confirmed coeliac disease should deter subsequent lower GI investigation 1

3. Colonoscopy is preferred over CT colonography for lower GI investigation 1

   • Both are superior to barium enema 1
   • Even if coeliac disease is found, still perform colonoscopy in patients >50 years, with marked anaemia, or significant family history of colorectal cancer 1

4. Small bowel investigation is not necessary unless:

   • Symptoms suggest small bowel disease 1
   • Haemoglobin cannot be restored/maintained with iron therapy 1

5. In recurrent IDA with normal OGD and colonoscopy: eradicate Helicobacter pylori if present 1

Critical pitfall: Faecal occult blood testing has no role in investigating IDA 1

Special Populations

Premenopausal women: Heavy menstrual bleeding is the most common cause, but still investigate if iron deficiency is confirmed 1, 2

Inflammatory bowel disease patients:

• Measure B12 and folate at least annually 1
• More frequent monitoring needed with small bowel disease/resection 1
• Ileal resection increases risk of B12 deficiency 1

Chronic kidney disease patients:

• Erythropoietin deficiency is the primary mechanism 1
• Functional iron deficiency may occur despite normal/elevated ferritin 1, 2

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Treatment Strategies

Iron Replacement

All patients require iron supplementation to correct anaemia AND replenish body stores 1:

Oral iron (first-line):

• 60-200 mg elemental iron daily, divided into 2-3 doses 2
• Take on empty stomach with vitamin C to enhance absorption 2
• Avoid concurrent tea, coffee, calcium, or antacids (impair absorption) 2

Intravenous iron indications 1:

• Oral iron not tolerated 1
• Inflammatory bowel disease (oral iron poorly effective) 1
• Chronic kidney disease with functional iron deficiency 1

Critical pitfall: Do not discontinue iron therapy when haemoglobin normalizes—continue until iron stores are replenished 2

Vitamin B12 Deficiency

For pernicious anaemia or malabsorption 3:

• 100 mcg intramuscular/deep subcutaneous daily for 6-7 days 3
• Then alternate days for 7 doses 3
• Then every 3-4 days for 2-3 weeks 3
• Maintenance: 100 mcg monthly for life 3

Critical warning: Vitamin B12 deficiency progressing >3 months produces permanent spinal cord degeneration 3. Patients must understand they require lifelong monthly injections 3.

Dangerous pitfall: Folic acid >0.1 mg/day may correct anaemia in B12 deficiency but allows irreversible neurologic damage to progress 3. Never give folic acid without confirming B12 status 3.

Folate Deficiency

Treat confirmed folate deficiency to avoid anaemia 1. Administer concomitantly with B12 if both deficiencies present 3.

Anaemia of Chronic Disease/Inflammation

Optimize treatment of the underlying disease first 1:

• In IBD, optimizing disease control (e.g., with infliximab) significantly improves haemoglobin independent of other interventions 1

Erythropoiesis-stimulating agents (ESAs) 1:

• Consider only after intravenous iron AND optimized disease therapy 1
• Target haemoglobin should not exceed 12 g/dL 1
• In critical care, use ESAs especially after trauma if no contraindications 1

Critical pitfall: Avoid routine iron therapy in critical care patients except when used with erythropoietin 1

Blood Transfusion

Restrictive transfusion strategy is strongly recommended 1:

Transfusion thresholds:

• Hb <7 g/dL in haemodynamically stable patients 1
• Hb <7.5 g/dL with clinical symptoms or cardiovascular instability 1
• Higher thresholds for patients with ischaemic heart disease, older age, or significant comorbidities 1

Single-unit transfusion policy 1:

• Transfuse one unit, reassess, then decide if additional units needed 1
• Each 400 mL unit increases Hb by ~1.5 g/dL 1

Critical principle: Blood transfusions are reserved for cardiovascular instability or severe symptomatic anaemia 1. They do not address underlying pathology and provide only transient correction 1. Always follow transfusions with intravenous iron supplementation 1.

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Prevention in Critical Care

Implement phlebotomy reduction strategies to prevent iatrogenic anaemia 1:

• Minimize blood sampling frequency 1
• Use paediatric collection tubes when appropriate 1
• Coordinate laboratory testing to reduce draws 1

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Common Pitfalls Summary

1. Do not rely solely on serum iron levels—they have significant diurnal variation and can be normal in early iron deficiency 2
2. Do not overlook iron deficiency in patients with normal haemoglobin 2
3. Do not use faecal occult blood testing to investigate IDA 1
4. Do not give folic acid without confirming B12 status in macrocytic anaemia 3
5. Do not stop investigating after finding one cause—dual pathology occurs in 1-10% of patients 1
6. Do not use blood transfusion as chronic anaemia treatment—it does not address underlying pathology 1, 4