The Blood Type Test (ABO, Rh) determines your blood type. It identifies your blood group (A, B, AB, or O) and whether your blood is Rh positive or Rh negative. - People whose red blood cells have A antigens are in blood group A. - Those with B antigens are in group B. - Those with both A and B antigens are in group AB. - Lastly, those who do not have either of these markers are in blood group O. The Rh factor (rhesus factor) is a protein on the surface of red blood cells. If the Rh protein is present, a person’s blood type is Rh+ (positive). If it is absent, the person’s blood is type Rh- (negative). This protein plays a role in determining whether the blood of two different people can be mixed. Blood type affects what blood you can receive or donate. The Blood Type Test does not require fasting.