22nd May 2023

Aetiology of anaemia

The World Health Organisation defines anaemia as a haemoglobin level <120g/L for women and <130g/L for men. Due to variations in normal haemoglobin ranges with age and sex, as well as between laboratory instruments, anaemia is widely defined as a haemoglobin below the reference range provided by the testing laboratory.

Haematopoeitic stem cells in the bone marrow differentiate into reticulocytes, which in turn are released into the circulation to develop into mature red blood cells. The average lifespan of a red blood cell is 120 days before it is removed from the circulation by macrophages.

Anaemia can present clinically with pallor of skin and mucous membranes, tiredness, exertional dyspnoea, palpitations, dizziness, exacerbation of existing angina or heart failure, or symptoms of the underlying cause of anaemia.

Anaemia can be classified by mechanism or by morphology. Mechanisms of anaemia include:

• Decreased production of red blood cells
• Increased loss of red blood cells
• Dilutional

Classification of anaemia by morphology is more commonly used clinically and is defined by the size of red blood cells, measured by mean corpuscular volume (MCV):

• Macrocytic (MCV>100fL)
• Normocytic (MCV 80-100fL)
• Microcytic (MCV<80fL)