Intended for healthcare professionals

Student Education

Essential haematology

BMJ 2004; 329 doi: (Published 01 November 2004) Cite this as: BMJ 2004;329:0411404
  1. Stephen French, preregistration house officer1,
  2. Arun Kochhar, third year medical student2
  1. 1St Thomas' Hospital, London
  2. 2Guy's, King's, and St Thomas' School of Medicine, London

Stephen French and Arun Kochhar explain how to interpret blood results

The full blood count is one of the most common medical investigations, and it can give important information to help support or refute a diagnosis that doctors have made based on clinical history and examination. The full blood count gives information about red cells (erythrocytes), white cells (leucocytes), and platelets.

Normally the cell counts are maintained in a steady state because the number produced by bone marrow (in haemopoiesis) is similar to the number destroyed by the reticuloendothelial system (the spleen, liver, and bone marrow). When this steady state is disrupted, cell counts may become abnormally increased or decreased.

Red cells

Red blood cells have a lifespan of about 120 days, in which they transport oxygen from the lungs to body tissues and carbon dioxide back to the lungs. The kidneys produce the hormone erythropoietin, which stimulates the bone marrow to produce red blood cells.

Anaemia occurs if the concentration of haemoglobin falls below the reference range for the age and sex of a person and arises from an imbalance between production and destruction of red cells. Symptoms of anaemia depend on how long the anaemia has been present and how severe it is. Symptoms can vary greatly between people and may include tiredness, decreased exercise tolerance, and shortness of breath. Pallor (paleness) of the conjunctiva indicates anaemia.

Anaemia can be simply classified according to the mean cell volume as microcytic (<76 fl), normocytic (76-96 fl), or macrocytic (>96 fl). This helps to determine the cause of the anaemia.

Microcytic anaemias result from defects in haemoglobin synthesis, the most common cause of which is iron deficiency. Common causes include chronic blood …

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