White blood cells

There are several main types of white blood cell.


About 70 per cent of white blood cells are phagocytes. Phagocytes engulf and destroy unwanted microorganisms that enter the blood, by the process of phagocytosis. They are part of the body's immune system.



Lymphocytes make up about 25 per cent of white blood cells. They are also part of the body's immune system. Lymphocytes produce soluble proteins called antibodies when a foreign body such as a microorganism enters the body.


Platelets are cell fragments produced by giant cells in the bone marrow.

Platelets stop bleeding in two main ways:

  • they have proteins on their surface that enable them to stick to breaks in a blood vessel and clump together
  • they secrete proteins that result in a series of chemical reactions that make blood clot, which plugs a wound.

Blood products

Blood products are components of blood that are given to a patient by transfusion. They include:

  • red blood cells
  • platelets
  • plasma
  • antibodies

Blood products are produced from blood from blood donors.

Blood products can then be given to patients depending on their needs. Patients rarely receive transfusions of whole blood in modern medicine.

Blood products are screened for:

  • infectious agents such as HIV
  • their blood group
  • the presence of certain antibodies

Blood for transfusion must be compatible with that of the patient's blood, for instance, their blood group. Before a transfusion, white blood cells are often removed to reduce the risk of infections or immune reactions.

Looking at blood cells

Many types of blood cell are 10 μm in size or less. You will need high power to examine them.

Diagram showing red and white blood cells. There are more red than white

The slides will have been stained to show the cells, and cell features. The micrograph shows many red blood cells and three white blood cells.

An example of a commonly-used stain is Giemsa stain. It aids identification by staining:

  • red blood cells pink
  • platelets pale pink
  • white blood cell cytoplasm pale blue
  • white blood cell nuclei magenta