I’ve just watched a drama documentary on TV that explains how important blood donations are. They are used for blood transfusions, and only certain blood types can be transfered between donor and  recipient. I decided to look up more information. See below.

From Google :

“The eight most common blood types are A+, A-, B+, B-, O+, O-, AB+, and AB-. These types are determined by the presence or absence of the Rh factor protein and the A and B antigens:

• Rh factor: If the Rh factor protein is present, the blood type is RhD positive (+), and if it’s absent, the blood type is RhD negative (-).
• A and B antigens: These antigens determine whether the blood type is A or B. 

There are also many other blood group systems, including the Duffy, K antigen (Kell), Lutheran, and Kidd blood groups. The International Society for Blood Transfusion has identified 42 blood-group systems in addition to the ABO and Rh systems. 

When matching blood types for a transfusion, it’s important to consider not only the A, B, and Rh antigens, but also minor antigens that aren’t routinely detected during blood typing. A process called cross-matching can help detect these minor antigens. “

See : http://blood.co.uk to arrange to donate.