Blood groups are called as positive due to the presence of Rh (Rhesus) factor on the blood cells.
True
Rhesus (Rh) factor is a protein found on the surface of RBC. If the blood has Rh protein then the blood is said to be positive. For example, A+, B+, AB+ ,O+. If the Rh factor is not present, then the blood group is called, negative blood group. The first basic blood test for finding the antigen was performed on the rhesus monkey, hence the name was given as Rhesus factor.