What does it mean to write a plus sign after A+ when writing blood type?

When writing blood type, the plus sign after A+ is the abbreviation of Rh(+). A+ is type A positive blood.

Rh(+) is a symbol in the Rh blood group system, which means the blood group system of rhesus monkeys, and it is a human blood group system, which can be divided into negative and positive.

When a person's red blood cells have blood group D substances (antigens), it is called Rh positive, which is expressed by Rh(+); When the D antigen is missing, it is Rh negative, which is expressed by Rh(-). Most people are positive. Rh system is probably the most complicated system in red blood cell blood group, and its importance is second only to ABO system.

Extended data:

Rh negative blood is called panda blood. According to cultural archaeology, physiological evolution, ethnic distribution and molecular clock theory, it may be the blood type of ancient people in Daxizhou. Their evolutionary route is different from that of farmers in Kroma. Neanderthals entered western Europe directly from North Africa and quickly occupied the continent.

The first prehistoric civilization was established by leaps and bounds. Perhaps it was because of a flood at the end of the ice age more than 10 thousand years ago that their civilization was completely destroyed and some people fled from Oceania to Western Europe. Later, farmers from Kroma entered Europe, merged with people from Daxizhou, and Rh-negative blood gradually dispersed.

Baidu encyclopedia -Rh blood group system