It has long been said that the blood type O negative was a universal blood donor type – meaning anyone, no matter what their blood type, could receive this type of blood. While type O negative can be given to anyone, there are still risks involved.
According to the Mayo Clinic, type O negative blood may have antibodies that can cause serious reactions.
To reduce the risks, ideally donated blood will be an exact match – both in the type and the rhesus factor -- with the person receiving it.
To make sure there is no reaction, small samples of the donated blood and the recipient’s blood are crossmatched to check for compatibility. However, in an emergency situation, type O negative blood can be given to anyone.