Unit D

Module 8 ~ Lesson 2

Rh Factor

In addition to the ABO blood typing system, the presence or absence of the Rh factor (antigen) determines if an individual is Rh positive or Rh negative. An Rh+ individual has the Rh antigen on his or her blood cells, while an Rh- individual will lack Rh antigens. The Rh system was named after the rhesus monkey since these monkeys were used to research blood typing.

A problem can arise if Rh- individuals are exposed to Rh+ blood. This typically happens when a pregnant woman (Rh- ) gives birth to a baby who carries the Rh antigen because blood often mixes during childbirth. Once the mother is exposed to Rh+ blood, her body will identify this blood as a foreign substance and create Rh antibodies.

In possible subsequent pregnancies, where a baby is again Rh+, the mother's antibodies may cross the placenta and endanger the child. A condition referred to as hemolytic disease of the newborn (HDN) can occur.

The Rh+ antibodies from the mother will begin destroying the baby's blood cells and can lead to brain damage, deafness, and death.




Blood Compatibility

To determine a person's blood type only a drop of blood is required. Anti-serums are added to each drop to determine the antigens on the person's blood cell. Although there are many identifying antigens on red blood cells, for the purpose of transfusion, only the ABO and Rh groups are tested. If the blood clumps with the anti-serum, it indicates the presence of that antigen on the red blood cells.

If an antigen is absent on the surface of a person's red blood cell, the corresponding antibodies are present in the serum. For example, Rh- individuals have Rh antibodies in their serum that will recognize and bind to a red blood cell with Rh antigens causing agglutination or clumping of the blood. This prevents a donor from receiving blood types for which they have antibodies.

The patient whose blood is pictured here would be able to receive blood from donors of type O+ or O-. Since he has the Rh factor, he does not produce the Rh antibody and can receive blood from Rh+ or Rh- donors. Since he does not have an A or a B antigen, he produces both anti-A and anti-B antibodies preventing him from receiving blood with those types of antigens.
The sample below shows no clumping with anti-A or anti-B serum, so it does not have either antigen. Anti-D is the antibody for the Rh factor. The test did clump with anti-D, therefore has the Rh factor. Nathan's blood type is O+.

Nathan. (May 6, 2008). Blood Type Test Results: O Positive. CC-BY-NC-ND Retrieved from www.flickr.com