Everyone’s blood seems to look the same, but when magnified beneath the lens
of scientific devices, there are some differences. The four main blood types
are A, B, AB, and O, but in the final analysis there are actually 8
distinct blood types.
A Rh-positive (34% of
the population)
A Rh-negative (6% of
the population)
B Rh-positive (9% of
the population)
B Rh-negative (2% of
the population)
AB Rh-positive (3% of
the population)
AB Rh-negative (1% of
the population)
O Rh-positive (38% of
the population)
O Rh-negative (7% of
the population)
(The above numbers are an approximation for the United
States population. Distribution may be
different among specific ethnic and/or racial groups.)
Early in the 20th century, Karl Landsteiner, an Austrian scientist who won a
Nobel Prize for his achievements, observed two distinct molecules present on
the surface of red blood cells. They are called antigens and are the
markers used to determine a person’s blood type. The two molecules were simply labeled
“A” and “B.”
Type A blood has A antigens
covering the red blood cells.
Type B blood has B antigens.
Type
AB blood has both A and B antigens.
Type O blood has neither.
Rh Antigen
There is also the Rh antigen which some people have and others don’t.
The blood cells that do have it are marked RhD positive. So “B+” means the
blood has B antigens and Rh antigens, and “B-“ follows suit with B antigens but
no Rh antigens. Approximately 84% of the population is Rh positive.