Blood Typing

Objectives

·      Describe the antigen-antibody reactions of the ABO and Rh blood groups

·      Be able to type a sample of unknown blood to determine the ABO and Rh blood types

·      Explain the clinical importance of blood types on pregnancy and transfusions

Blood Typing

[Section 18.6.1: Blood Typing; Antigens, Antibodies, and Transfusion Reactions]

Each blood type is a function of the presence or absence of specific molecules, called antigens, on RBCs

Antigens are molecules that your body can use to differentiate self and non-self (virtually all proteins, carbohydrates, etc. are types of antigens). People with different blood types have RBCs with different antigens on them.

Antibodies are produced in response to some antigens (non-self), and are generally used by the immune system to recognize and remove foreign objects that don’t belong. 

**Antibodies and antigens in an individuals blood do not interact with one another, but what happens when you mix blood/antibodies from different people?**

More than 50 blood types in human population

The most clinically significant are the ABO and Rh(+/-) blood groups

The ABO Blood Group

[Section 18.6.2: The ABO Blood Group]

ABO typing does NOT affect a person’s Rh designation

Type A blood= “A” antigens on cell, anti B antibodies

Type B blood= “B” antigens on cell, anti A antibodies

Type AB= “A” and “B” antigens on cell, no antibodies

Type O blood= no antigens on cell, anti A and B antibodies

If a different type of blood is put into your bloodstream, the blood will agglutinate (clump) and hemolysis (bursting) occurs within the foreign blood cells

Rh Blood Group

[Section 18.6.3: Rh Blood Groups]

Named after Rhesus monkey where it was first identified

Rh positive (+)  contains a D-antigen

Rh negative (-) has no D-antigen, and unlike A/B/O,  no anti-D-antibodies are present in Rh negative individuals

Grouped with ABO blood group to identify a blood type (example A+, B-, O-)

The Rh group only has ONE antigen (the D antigen) and ONE antibody (anti D) that could be present.

            If RBCs have a D antigen, the blood is positive

            If RBCs have no D antigen, the blood is negative

            Negative blood DOES NOT have anti D antibodies!

If positive and negative blood is mixed in an Rh(-) individual, anti D antibodies will be produced against the Rh(+) blood after a short while (a couple weeks)

Mixing of Rh positive and negative will result in production of anti D antibodies

You can get away with it once because anti-D antibodies don’t exist beforehand, but a second time will cause a reaction

Importance of Rh during Pregnancy

[Section 18.6.3: Rh Blood Groups]

[Figure 18.15: Erythroblastosis Fetalis]

This is VERY important during childbirth. If the mother is Rh-negative, but her child is Rh-positive and any internal bleeding from the Rh(+) child occurs, the mothers blood will begin producing anti-D antibodies which will then hemolyze her babies blood (and any future Rh(+) fetuses).  Exposure of the babies blood during childbirth can also be problematic for future Rh(+) fetuses

This is called  hemolytic disease of the newborn or erythoblastosis fetalis

RhoGam a dosage of anti-D antibodies is given to the mother at 28 weeks and within 72 hours of giving birth in order to destroy any fetal blood cells in her blood so she will not produce her own anti-D antibodies.  RhoGam antibody dosage is small enough not to hurt fetus, but strong enough to keep mom’s immune system from attacking baby

Determining Blood Type

[Section 18.6.4: Determining ABO Blood Types]

[Figure 18.16: Cross Matching Blood Types]

To determine blood types, anti-serum is used.

The serum contains either anti-A antibodies or anti-B antibodies which react to the antigens on the RBC surface

If using anti A anti serum and the blood sample clumps:

 then the blood could be Type A, or Type AB

You would then test with anti B anti serum

If it does clump, the blood is Type AB, if it doesn’t then it is Type A.

Make sure to NEVER mix anti serums or blood samples!

Transfusions

[Section 18.6.5: ABO Transfusion Protocols]

[Figure 18.17: ABO Blood Group]

The first blood transfusions used animal blood as a source of blood

This often resulted in severe allergic reactions, and often death

In human transfusions, additional complications can arise when the donor’s antibodies react with the recipient’s RBCs, and vice versa

Thus, only donor RBCs are transferred, no antibodies

Type O- is considered the universal donor

Type AB+ is considered the universal recipient

An incorrect transfusion could cause blood to agglutinate within the recipient’s blood vessels