Blood groups

What is blood?

Your body carries aroundfourto six litres (7to 10.5 pints) of blood. Blood is made up of red blood cells, white blood cells and platelets in a liquid called plasma.

Plasma is about 90% water, but also contains proteins, nutrients, hormones and waste products. Blood is made up of about 60% plasma and 40% blood cells.

Each type of blood cell has a specific role to play:

red blood cells carry oxygen around the body and remove carbon dioxide and other waste products; they give blood its red colour
white blood cells are part of the immune system (the body's natural defence mechanism) and help fight infection
platelets help the blood clot (thicken) to stop bleeding

Medically Reviewed by a doctor on 21 Dec 2018

Articles for blood groups

Introduction

There are four different blood types, known as blood groups. The four main blood groups are A, B, AB and O.

What is blood?

Your body carries aroundfourto six litres (7to 10.5 pints) of blood. Blood is made up of red blood cells, white blood cells and platelets in a liquid called plasma. Plasma is about 90% water, but als

Antigens and antibodies

Your blood group is identified by antigens and antibodies in the blood. Antibodies are part of your body's natural defences against invading substances such as germs. Antigens are protein molecules f

The ABO system

There are four main blood groups defined by the ABO system: blood group A has A antigens on the red blood cells with anti-B antibodies in the plasma blood group B has B antigens with anti-A ant

Red blood cells sometimes have another antigen, a protein known as the RhD antigen. If this is present, your blood group is RhD positive. If it's absent, your blood group is RhD negative. This means y

Blood group test

To work out your blood group, your red cells are mixed with different antibody solutions. If, for example, the solution contains anti-B antibodies and you have B antigens on your cells (you are blood

Pregnancy

Pregnant women are always given a blood group test. This is because if the mother is RhD negative but the child has inherited RhD-positive blood from the father, it could cause complications if left u

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