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Types & Rh System

Everyone's blood has a combination of elements from the different systems that classify blood. Two of these blood group systems are the ABO system and Rh system. The group you belong to depends on the presence or absence of proteins and sugars called antigens on the surface of your blood cells as well as the proteins called antibodies in the watery part of your blood. Not all blood types are compatible.

  • There are four major blood groups A, O, B, and AB divided into Rh Positive and Rh Negative types: A (Rh Positive); A (Rh Negative); O (Rh Positive); O (Rh Negative); B (Rh Positive); B (Rh Negative); AB (Rh Positive); and, AB (Rh Negative).

  • The most common blood type in Canada is O Rh Positive (approximately 39 per cent of Canadians have O Rh Positive blood). The rarest blood type is AB Rh Negative (only about one per cent of Canadians have AB Rh Negative blood). All blood types are needed to meet the needs of patients for blood and blood products.

People with O Rh Negative blood are considered universal donors because patients of all blood types can receive O Rh Negative blood.

Blood Types and Patient/Donor Compatibilities

Blood Type
% of Blood Type Amongst all Canadians Patient Types Compatible with the Red Blood Cells of Donor Patient Types Compatible with the Plasma of Donor
(Rh not indicated)
A+ 36 A+, AB+ A, O
A- 6 A-, A+, AB-, AB+ A, O
O+ 39 O+, A+, B+, AB+ O
O- 7 All Blood Types O
B+ 7.6 B+, AB + B, O
B- 1.4 B-, B+, AB-, AB+ B, O
AB+ 2.5 AB+ All Blood Types
AB- 0.5 AB-, AB+ All Blood Types

Understanding Blood Antigens

At the genetic level, each person has two genes that determine his/her ABO blood type. The two genes carried by an individual are passed on from his/her parents. Although each parent also has two genes, they both contribute only one. This process of combining genes, one from each parent, can sometimes lead to children with different blood types than their parents. To discover the possible blood types of potential offspring, it is necessary to know the two genes of each of the parents.


A and O genes
Type A blood

B and O genes
Type B blood

A and O genes
Type A blood

A and B genes
Type AB blood


O and O genes
Type O blood


O and B genes
Type B blood

A person with type A blood could have two A genes or one A gene and one O gene. Likewise, type B blood can result from a person with either two B genes or one B and one O gene. Type AB blood only occurs in a person with both A and B genes. People with type O blood have two O genes.

Blood Components
Types & Rh System
Blood Shelf Life
Blood Uses
From Vein to Vein
Where Does Blood Go?

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