Blood Groups and Transfusions

Blood Loss

• Body is only able to compensate for minor losses– 15-30% cause weakness– >30% body goes into shock• Can be fatal

• Transfusions used to replace lost blood

Blood Components• Whole blood– Contains both the RBCs and plasma from the donor

• Packed RBCs– Removal of the plasma from the RBCs

• Plasma (FFP)– Removed and frozen from RBCs

Blood Components• Donated blood relies on the honesty of the

donor (questionnaire) and lab testing to ensure it is safe to transfuse

• Many hemophiliacs in the early 1980’s were infected with HIV from transfusions

• MOST major diseases can be tested at the donation lab (red cross)

Human Blood Groups

• Plasma membrane on RBC contains antigens–Protein, genetically determined

–Used by body to identify “self”

–Antibodies recognize “foreign” antigens• Attack cells that are not “self”• Causes cells to agglutinate (clump)

Human Blood Groups• Blood transfused of wrong “type” can be fatal

(transfusion reaction)

• Type is based on the antigens on the RBC– ~30 antigens on RBC’s

• ABO antigens & Rh cause most severe reactions

ABO Blood Groups• Based on two antigens, Type A or Type B

• Each person inherits one allele from each parent– Co-dominant – both alleles show

• Type O is absence of BOTH antigens

A type A blood type may be AA or AOA type B blood type may be BB or BO

A type AB person inherited one of each

Human Blood Groups

ABO Blood Groups• Most immune responses require “sensitization”– Recognition of “foreign” antigens– Antibodies are produced after sensitization

• ABO blood groups do not work this way!– Antibodies to “foreign” ABO types are produced

during infancy.– Antibodies are made to “non-self” antigens• A type A person makes antibodies to B antigens

Rh Blood Groups• First identified in Rheus monkeys

• Made up of 8 antigens – Collectively called “D”

• Most Americans are Rh positive– They have ONE or more of the 8 antigens

• The Rh system must be sensitized before antibodies are made

Rh Blood Groups

• Rh negative form antibodies after exposed to Rh positive blood– Can occur because of transfusion– Can occur during pregnancy of a Rh negative mother with

a Rh positive baby

• Transfusion reactions to Rh do not occur to the first exposure– The second exposure will result in attack on the

RBC’s (hemolysis)

Rh Blood Groups

• Mothers are tested during pregnancy to determine Rh type

• Rh negative mothers are given RhoGAM after delivery– Prevents FUTURE reactions between Mom and Baby– Untreated results in hemolytic disease of the

newborn• Mom’s antibodies attack baby’s cells

Blood Typing

• Blood drawn to test ABO and Rh type• Centrifuged to separate into cells and plasma– CELLS have ANTIGENS– PLASMA has ANTIBODIES

• Incorrect blood typing that results in transfusions can be fatal

• Testing is done in a two step process to ensure correct types

Blood Typing• Forward Typing– Patient’s RBCs are mixed with a known solution

containing anitbodies • Antisera A or Antisera B

– Blood cells will agglutinate if the ANTIGEN is present on the person’s RBCs

– Clumping with Antisera A means that Antigen A is present (type A)• Clumping with Antisera B means Type B• Clumping with BOTH, Type AB

Blood Typing• Reverse Typing– The patient’s serum/plasma is tested using

KNOWN types of RBCs.– A drop of cells are added to the serum – A person who is type A will have antibodies to type B cells– A Type A person will agglutinate with Type B cells.

Blood Type Frequencies

Blood Typing• Rh is tested “forward” style using the patient’s cells• The patient’s cells are mixed with “Anti-D”

antiserum• Clumping with the Anti-D means the patient is Rh

positive.

• Both ABO/Rh testing is done in phases– At room temperature – And at 37°C

Blood Typing• Blood typing is typically done in a test tube or in

a more recent procedure using a gel apparatus • Forward and reverse typing allows for

discrepancies to be found

Cross Matching

• More than ABO/Rh matter in transfusions– ~30 antigens on the RBC– ABO/Rh are the MOST severe causes

• Blood from donor is mixed with patient plasma/serum to check for a potential reaction

• If no reaction occurs the unit is compatible and can be transfused

Cross Matching

• EVERY unit of blood MUST be cross matched

• If there is a reaction in the test tube, further investigation and testing must be done before the patient can be transfused– Involves testing for the MOST common antigens– Like a giant puzzle, you must eliminate each one

• If the lab cannot determine the cause of the reaction, the blood is sent to a blood center