What does O positive (O-type, RhD+) mean?

O-type RhD positive refers to blood group O in the ABO blood group system and RhD positive in the Rh blood group system.

There are dozens of classification systems for human blood types, among which two are commonly used in clinical practice: the ABO blood group system and the Rh blood group system. The ABO system divides human blood into four types: A, B, AB, and O, while the Rh system classifies blood as either RhD positive (RhD+) or RhD negative (RhD−). In the general population, the four ABO blood types are roughly equally distributed, whereas in the Rh system, RhD+ is common and RhD− is rare. Due to its rarity, RhD− blood is often referred to as "Panda blood." In the blood typing system, type O means that the red blood cells lack both A and B antigens, while the Rh factor refers to the presence of Rh antigens on the surface of red blood cells. If Rh antigens are present, the blood is Rh-positive; if absent, it is Rh-negative. Therefore, individuals with O-type Rh-positive blood have red blood cells that lack A and B antigens but carry Rh antigens. O-type Rh-positive is a relatively common blood type, accounting for approximately 38% of the population.

In addition, O-type RhD+ is a common blood type. Blood type and Rh factor compatibility are critically important in medical procedures such as blood transfusions and organ transplantation, as mismatches between different blood types or Rh factors may trigger immune reactions, leading to adverse outcomes such as transfusion reactions.