-positive is a qualification given in association with the Rh (Rhesus) blood group system, one of the principal blood group systems, along with the ABO system, which enables a precise blood typology to be established. Every person is either Rh-negative, or Rh-positive, allowing for the determination of blood transfusion compatibility. The Rh-positive type is by far the most common, with around 85% of the Caucasian population estimated as having a positive blood type (0+, A+, B+, or AB+). People with Rh+ can give their blood to others with Rh+, but not to those with Rh-, as this leads to a reaction in the receiving person's body. Rhesus-positive people can, however, receive blood from Rhesus-negative donors.