Blood Transfusion (cont.)

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What are the different types of blood?

Almost all cells, including red blood cells, have molecules on their surface that have important roles to play in interactions with cells of the immune system. There are multiple sites on each cell for the molecules, and at each site one of several related molecules may reside. Each site has only a limited number of different molecules that can reside there; each site has its own, unique molecules. Each molecule that can reside at any one site is referred to (defined) as a blood type, and the entire group of related molecules that can occupy a single site is referred to as a blood group.

A blood group is an inherited feature. For example, two series of blood types constitute a blood group system known as the Rh or the ABO systems.

Because blood types are responsible for the interactions between cells such as red blood cells and the immune system, it is important that the blood types of the donor and the recipient of red blood cells match. If the donor and recipient's blood types are not matched, the recipient's immune system will destroy the donor's cells.

Blood types

There are four blood types:

  1. A,
  2. B,
  3. AB, or
  4. O.

Every person has one of the above four blood types. In addition, each person's blood is either:

  • Rh-positive, or
  • Rh-negative.

So, for example, if a person has type A blood, it's either type A positive or type A negative.

Type O blood - universal donors

  • Type O negative blood is safe for just about everyone. People with type O negative blood are referred to as universal donors; and type O negative blood is used for emergencies in which there is no time to test a person's blood type.

Type AB blood - universal recipients

  • Individuals who have type AB positive blood are referred to as universal recipients. This means that they can receive any type of blood.

Rh-positive and Rh-negative

  • People who have Rh-positive blood can receive Rh-positive or Rh-negative blood.
  • If a person has Rh-negative blood, they should only receive Rh-negative blood.
  • Rh-negative blood is used for emergencies when there is not time to test a person's Rh type.
Medically Reviewed by a Doctor on 5/11/2015

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