What is the most common blood type? Here's which is most (and least) common.

A person's blood type is determined by "the presence or absence of certain antigens – substances that can trigger an immune response if they are foreign to the body," according to American Red Cross.

Four major blood groups exist and are categorized by the presence or absence of two antigens, A and B, on the surface of red blood cells. Additionally, there is a protein called "the Rh factor," which can also be present (+) or absent (–).

These factors help define the eight most common blood types: A positive, A negative, B positive, B negative, O positive, O negative, AB positive and AB negative, says the Red Cross. But of these eight, which is the most common?

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What is the most common blood type?

According to the American Red Cross, the most common blood type is O positive, which is the blood type for 37% of the population. This blood type is in high demand since it is "the most frequently occurring blood type."

The second most common blood type is A positive which occurs in "33% of Caucasian, 24% of African American, 27% of Asian and 29% of Latino American" populations," says the Red Cross.

What is the rarest blood type?

There are over 600 other known antigens, and the absence or presence of them creates "rare blood types," says the American Red Cross.

However, statistically, AB negative is rarer than other blood types, only occurring in "1% of Caucasian, 0.3% of African American, 0.1% of Asian and 0.2% of Latino American" populations.

The blood type of B negative is also uncommon, occurring in "2% of Caucasian, 1% of African American, 0.4% of Asian and 1% of Latino American" populations, says the Red Cross.

What is the rarest blood type? Here is the least common of the eight blood types

What is the 'golden blood' type?

Rh-null is the rarest blood type and is considered to be "golden blood," according to Discovery. Rh-null blood is categorized by "a complete lack of antigens in the Rh system, which is the largest blood group system."

Only 43 people on Earth have ever been recorded to have this blood type, and there are only nine active donors, says Discovery.

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This article originally appeared on USA TODAY: What is the most common blood type? Blood types and facts