The term Rhesus (Rh) blood group system refers to the 5 main Rhesus antigens (C, c, D, E and e) as well as the many other less frequent Rhesus antigens. The terms Rhesus factor and Rh factor are equivalent and refer to the Rh D antigen only. Individuals either have, or do not have, the Rhesus factor (or Rh D antigen) on the surface of their red blood cells.
- Presence of the Rhesus factor is usually indicated by the 'RhD positive' suffix to the ABO blood type.
- Absence of the Rhesus factor is usually indicated by the 'RhD negative' suffix to the ABO blood type.
- The Rhesus system is named after the Rhesus Macaque.