Anaemia is the presence of reduced haemoglobin in the blood. Formally, the World Health Organizatiοn (WHO) defines anaemia by the haemoglobin concentration in the blood according to age and sex ¹:

• adult men: <130 g/L

• adult women: <120 g/L

Values for pregnant women and children are different.

Clinical presentation

The clinical features of anaemia vary depending on the severity and underlying cause, and when present, can be subtle. General clinical features may include fatigue, dyspnoea, pallor of mucous membranes, and tachycardia ².

Pathology

Aetiology

The aetiology of anaemia is traditionally categorised by the volume of the red cell, i.e. the mean cell volume (MCV), into microcytic (MCV <82 fL), normocytic (MCV = 82-98 fL) and macrocytic (MCV >98 fL) anaemias ². It should be noted that some causes of anaemia may overlap between these categories.

Microcytic (MCV <82 fL)

• iron deficiency anaemia (IDA): most common cause of anaemia

• anaemia of chronic disease: second most common cause of anaemia

• thalassaemia

• copper deficiency: very rare

• sideroblastic anaemia: very rare

• lead poisoning: very rare

• zinc poisoning: very rare

Normocytic (MCV 82-98 fL) 

• dietary anaemia: mixed iron, vitamin B₁₂, and/or folate deficiencies

• acute blood loss

• chronic kidney disease

• haemolytic anaemia

  • intrinsic: membranopathy, enzymopathy, haemoglobinopathy

  • extrinsic: immune-mediated, microangiopathic, associated with infection, chemical agent (spider venoms), metabolic

• anaemia of chronic disease

• bone marrow disease

  • aplasia

    • idiopathic

    • paroxysmal nocturnal haemoglobinuria (PNH)

    • Fanconi syndrome

  • pure red cell aplasia

    • congenital (e.g. Diamond-Blackfan syndrome)

    • acquired (e.g. post-parvovirus B19)

  • myelodysplastic syndrome

  • secondary bone marrow disease

    • infiltrative disease: metastases, lymphoma

    • drugs

    • toxins e.g. selenium

    • irradiation

    • infective: viral

    • immunological

Macrocytic (MCV >98 fL)

• megaloblastic

  • dietary deficiency: vitamin B₁₂, folate

  • thiamine-responsive megaloblastic anaemia syndrome

  • orotic aciduria

  • medication: hydroxyurea, azathioprine, methotrexate

• non-megaloblastic

  • reticulocytosis

  • hypothyroidism

  • cirrhosis

  • myelodysplastic syndrome

  • pure red cell aplasia

See also

• polycythaemia

• cyanosis

• haemoglobin