Blood types are determined by genetics. The distribution of blood types varies from country to country, depending on the ethnic background of the population.

There are four main blood types: A, B, AB, and O. The graphic at left shows the current distribution of these four blood types in America.

 

 

Each of the blood types is either RH positive (+) or Rh negative (-). The chart below shows the distribution of these blood types in America:

Blood Type Distribution in America
Blood Type	% of Population	Blood Type	% of Population
O+	39%	O-	9%
A+	31%	A-	6%
B+	9%	B-	2%
AB+	3%	AB-	1%

The blood type of a patient determines which blood types they are able to receive as a transfusion. To see general information about blood types, click here.