Anemia is the presence of reduced hemoglobin in the blood. Formally, the World Health Organizatiοn (WHO) defines anemia by the hemoglobin 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 anemia vary depending on the severity and underlying cause, and when present, can be subtle. General clinical features may include fatigue, dyspnea, pallor of mucous membranes, and tachycardia ².

Pathology

Etiology

The etiology of anemia is traditionally categorized 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) anemias ². It should be noted that some causes of anemia may overlap between these categories.

Microcytic (MCV <82 fL)

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

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

• thalassemia

• copper deficiency: very rare

• sideroblastic anemia: very rare

• lead poisoning: very rare

• zinc poisoning: very rare

Normocytic (MCV 82-98 fL) 

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

• acute blood loss

• chronic kidney disease

• hemolytic anemia

  • intrinsic: membranopathy, enzymopathy, hemoglobinopathy

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

• anemia of chronic disease

• bone marrow disease

  • aplasia

    • idiopathic

    • paroxysmal nocturnal hemoglobinuria (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 anemia syndrome

  • orotic aciduria

  • medication: hydroxyurea, azathioprine, methotrexate

• non-megaloblastic

  • reticulocytosis

  • hypothyroidism

  • cirrhosis

  • myelodysplastic syndrome

  • pure red cell aplasia

See also

• polycythemia

• cyanosis

• hemoglobin