Anaemia

HB/MCV Results

HB (Reference range: 133-167 ×10⁹/L)

MCV (Reference range: 82-98 ×10⁹/L)

 

What is Microcytic Anaemia?

Microcytic anaemia is defined as a low haemoglobin (Hb) with a reduced mean corpuscular volume (MCV < 80 fL). It typically reflects iron deficiency, but other causes include chronic disease and thalassaemia traits.

Common Causes

  • Iron deficiency anaemia (e.g. blood loss, poor intake)
  • Anaemia of chronic disease (inflammatory block of iron utilisation)
  • Thalassaemia trait (genetic)
  • Sideroblastic anaemia (rare)
  • Lead poisoning (very rare in UK)

Stepwise Clinical Approach

Step 1: Confirm and Repeat

Ensure low Hb and low MCV are consistent across two samples to exclude lab error or dilution effects.

When repeating, also request:

  • Iron studies (Ferritin, Iron, TIBC): to confirm iron deficiency
  • CRP: to identify inflammation that may falsely elevate ferritin
  • Haemoglobin electrophoresis: to detect thalassaemia or haemoglobinopathies if iron studies normal
  • Reticulocyte count: to assess marrow response
  • Coeliac screen: if iron deficiency confirmed without obvious cause (e.g. no bleeding)

These investigations help clarify the underlying cause and guide management.

Step 2: Identify Common Patterns

  • Low ferritin + low iron: iron deficiency anaemia
  • Normal/high ferritin + low iron: anaemia of chronic disease
  • Normal iron studies, abnormal electrophoresis: thalassaemia trait

CRP helps interpret ferritin: it is an acute phase reactant.

Step 3: Consider Underlying Causes

  • Gastrointestinal bleeding (e.g. menorrhagia, peptic ulcer, malignancy)
  • Malabsorption (e.g. coeliac disease)
  • Chronic kidney disease (may contribute to anaemia of chronic disease)
  • Inherited conditions (e.g. thalassaemia)

Important: in men with confirmed iron deficiency anaemia, always request a FIT (faecal immunochemical test) to screen for occult gastrointestinal blood loss.

Step 4: Monitor or Refer

  • Iron deficiency with clear cause: start oral iron replacement and recheck in 2-3 months
  • No obvious cause for iron deficiency (especially in men): refer for further investigation (e.g. gastroscopy, colonoscopy, FIT if not already done)
  • Suspected thalassaemia or sideroblastic anaemia: refer to haematology

Step 5: Red Flags Requiring Urgent Action

  • Severe anaemia (Hb < 80 g/L) or symptomatic anaemia (e.g. chest pain, syncope)
  • Evidence of gastrointestinal bleeding (e.g. melaena, haematemesis)
  • High suspicion of underlying malignancy

Urgent referral or hospital admission may be necessary depending on clinical stability.

 

What is Normocytic Anaemia?

Normocytic anaemia is defined as a low haemoglobin (Hb) with a normal mean corpuscular volume (MCV 80-100 fL). It often reflects underproduction, chronic disease, or acute blood loss.

Common Causes

  • Anaemia of chronic disease (e.g. inflammatory, infective, malignant)
  • Acute blood loss (e.g. trauma, gastrointestinal bleeding)
  • Chronic kidney disease (reduced erythropoietin production)
  • Bone marrow failure (e.g. aplastic anaemia, myelodysplasia)
  • Haemolysis (early stages)

Stepwise Clinical Approach

Step 1: Confirm and Repeat

Confirm persistently low Hb with a normal MCV to exclude transient dilutional effects or lab error.

When repeating, also request:

  • Reticulocyte count: to distinguish between underproduction (low reticulocytes) and blood loss/haemolysis (high reticulocytes)
  • CRP and ESR: to identify chronic inflammation or infection
  • Renal function tests (U&Es, eGFR): to assess for chronic kidney disease
  • Liver function tests: to exclude liver disease-related anaemia
  • Blood film: to assess for abnormal morphology or haemolysis features

These tests help identify whether anaemia is due to chronic disease, blood loss, marrow failure, or haemolysis.

Step 2: Assess the Likely Cause

  • Raised CRP/ESR: suggest anaemia of chronic disease
  • Low eGFR: indicates anaemia secondary to renal impairment
  • High reticulocyte count: suggests active blood loss or haemolysis
  • Low reticulocyte count: suggests marrow underproduction (e.g. aplasia)

Blood film may show fragmented cells in haemolysis or blasts in marrow disease.

Step 3: Consider Underlying Conditions

  • Chronic infections (e.g. tuberculosis, HIV)
  • Chronic inflammatory diseases (e.g. rheumatoid arthritis)
  • Chronic kidney or liver disease
  • Haematological malignancies (e.g. myelodysplasia)

Step 4: Monitor or Refer

  • Stable anaemia due to known chronic disease: monitor every 3-6 months
  • Unexplained normocytic anaemia: refer to haematology
  • Evidence of haemolysis, marrow failure, or malignancy: urgent referral

Step 5: Red Flags Requiring Urgent Action

  • Severe anaemia (Hb < 80 g/L)
  • Rapidly dropping Hb without obvious bleeding
  • Presence of blasts, abnormal cells, or pancytopenia on FBC
  • Signs of haemolysis (jaundice, dark urine)

Urgent referral to haematology or acute assessment may be necessary.

 

What is Macrocytic Anaemia?

Macrocytic anaemia is defined as a low haemoglobin (Hb) with an increased mean corpuscular volume (MCV > 100 fL). It is commonly caused by vitamin deficiencies, alcohol misuse, or bone marrow disorders.

Common Causes

  • Vitamin B12 deficiency
  • Folate deficiency
  • Alcohol misuse (most common reversible cause)
  • Liver disease
  • Hypothyroidism
  • Haematological malignancies (e.g. myelodysplasia)
  • Medications (e.g. hydroxycarbamide, methotrexate)

Stepwise Clinical Approach

Step 1: Confirm and Repeat

Confirm true macrocytosis and rule out mixed anaemia (e.g. iron deficiency + B12 deficiency).

When repeating, also request:

  • Vitamin B12 and folate levels: to detect nutritional deficiencies
  • Thyroid function tests (TSH, T4): to exclude hypothyroidism
  • Liver function tests: to assess for alcohol misuse or liver disease
  • Blood film: to look for hypersegmented neutrophils or abnormal cells
  • Reticulocyte count: to assess for marrow response or recovery

These tests help distinguish between reversible causes and serious marrow pathology.

Step 2: Assess the Likely Cause

  • Low B12 or folate: nutritional deficiency anaemia
  • Abnormal liver function: suspect alcohol-related or liver disease anaemia
  • Raised TSH (low T4): hypothyroidism-related anaemia
  • Blood film with blasts or dysplastic changes: consider myelodysplasia

Clinical history (e.g. alcohol use, diet) is essential to interpretation.

Step 3: Consider Underlying Conditions

  • Dietary insufficiency (e.g. veganism without supplementation)
  • Alcohol misuse
  • Gastrointestinal malabsorption (e.g. coeliac disease, pernicious anaemia)
  • Haematological malignancies or marrow failure

Step 4: Monitor or Refer

  • Identified reversible cause (e.g. B12 deficiency, alcohol): treat and recheck Hb/MCV in 8-12 weeks
  • No clear cause or blood film abnormalities: refer to haematology
  • Persistent or worsening macrocytosis despite treatment: escalate investigation

Step 5: Red Flags Requiring Urgent Action

  • Severe anaemia (Hb < 80 g/L) with symptoms
  • Neurological symptoms suggestive of B12 deficiency (e.g. paraesthesia, ataxia)
  • Blood film showing blasts or dysplastic features
  • Evidence of bone marrow failure (e.g. pancytopenia)

Urgent referral to haematology may be required if red flags present.

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