What are platelets?

Platelets are very small cells in the blood that are made by stem cells in the bone marrow. Together with clotting proteins, platelets are important for clotting of your blood.

Amount of platelets

An adult has between 150 and 400 billion blood platelets per litre of blood.


A blood platelet survives for about 10 days in your body.

Too few platelets

If someone has too few or dysfunctional platelets, spontaneous bleeding can occur. These bleeds usually occur in the skin and mucous membranes, but can sometimes occur internally.

This may be caused by treatment with chemotherapy or radiotherapy, for example. These treatments damage the stem cells and they are temporarily unable to make platelets.

Life-saving platelet transfusions

A transfusion of donor platelets can prevent these spontaneous, sometimes life-threatening bleeding. If a bleeding has already occurred, swift administration of platelets is life-saving.