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HealthInfo Canterbury

What blood is made of

Your blood is a mixture of blood cells and a liquid called plasma.

Blood cells

Blood is about 55% plasma, 4% white blood cells and platelets, and 41% red blood cells.Your blood cells are made in your bone marrow. You have three main types of blood cells:

Red blood cells (erythrocytes)

Red blood cells are what make your blood red. They contain a substance called haemoglobin, which carries oxygen around your body. You need iron, vitamin B12 and folic acid for these red blood cells to work properly. If you're low in red blood cells it's called anaemia.

White blood cells (lymphocytes)

White blood cells are part of your immune system. They help you fight infections. Infections are the most common cause of high white blood cells.

Platelets (thrombocytes)

Platelets are tiny cell fragments which, with clotting factor proteins, help your blood to clot if you get cut.


Plasma is a yellow liquid that contains many chemicals and proteins, which all do different things. They include clotting proteins, hormones, enzymes, antibodies, nutrients, sugars, and salts.

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Written by HealthInfo clinical advisers. Endorsed by clinical director, Haematology Department, Canterbury DHB. Last reviewed May 2020.

Page reference: 165782

Review key: HIBBV-38552