Everybody has one of 4 blood types (A, B, AB or O). You inherit your blood group from your parents. These blood types are further identified as being either positive or negative. For example, your blood type can be A positive or A negative. The ‘positive’ or ‘negative’ shows your 'Rhesus factor' (RhD), which identifies if you have a protein known as 'D antigen' on the surface of your red blood cells.