O negative is a universal blood donor, while o+ can only safely donate to other "positive" blood types. The + or - refers to the Rh factor in all types of blood, a specific blood antigen/antibody (called Rhesus factor--it's a protein). People who have an Rh factor on the red blood cell's surface are referred to as Rh + . Those who haven't are called Rh and Rh- blood does not have Rh antibodies naturally in the blood plasma. But a person with Rh- blood can develop Rh antibodies in the blood plasma if he or she receives blood from a person with Rh+ blood, because this can trigger the production of Rh antibodies (not a good thing-if pateint hasn't been sensitived to RH proteins in red blood cells ). However a person with Rh+ blood can receive blood from a person with Rh- blood without any problems.
So maybe the most important difference is that people of O- blood type are considered universal donors--they can donate to people of any of ABO blood combinations, whether or not the reciptient is RH negaqtive or positive. People of O+ can safely donate to A+, B+, O+ or AB+.
So maybe the most important difference is that people of O- blood type are considered universal donors--they can donate to people of any of ABO blood combinations, whether or not the reciptient is RH negaqtive or positive. People of O+ can safely donate to A+, B+, O+ or AB+.