Men can give blood a maximum of five times per year, women three times per year. How often you give blood will depend on your blood type.
Blood type 0 negative is used relatively often in hospitals. That is because blood with this blood type can be given to any patient in emergencies. Blood donors with this blood type are sometimes invited to donate more often.
When possible, we prefer to give patients blood of their own blood type. This means a patient with blood type AB positive will be given blood from an AB positive blood donor. That is why the Blood Bank needs all blood types.