Antigens are nonself molecules, usually large proteins, which provoke an immune response. In transfusion reactions, antibodies attach to antigens on the surfaces of erythrocytes and cause agglutination and hemolysis. ABO blood group antigens are designated A and B. People with type A blood have A antigens on their erythrocytes, whereas those with type B blood have B antigens. Those with AB blood have both A and B antigens, and those with type O blood have neither A nor B antigens. The blood plasma contains preformed antibodies against the antigens not present on a person’s erythrocytes.
A second group of blood antigens is the Rh group, the most important of which is Rh D. People with Rh− blood do not have this antigen on their erythrocytes, whereas those who are Rh+ do. About 85 percent of Americans are Rh+. When a woman who is Rh− becomes pregnant with an Rh+ fetus, her body may begin to produce anti-Rh antibodies. If she subsequently becomes pregnant with a second Rh+ fetus and is not treated preventively with RhoGAM, the fetus will be at risk for an antigen-antibody reaction, including agglutination and hemolysis. This is known as hemolytic disease of the newborn.
Cross matching to determine blood type is necessary before transfusing blood, unless the patient is experiencing hemorrhage that is an immediate threat to life, in which case type O− blood may be transfused.
ABO blood group
blood-type classification based on the presence or absence of A and B glycoproteins on the erythrocyte membrane surface
agglutination
clustering of cells into masses linked by antibodies
cross matching
blood test for identification of blood type using antibodies and small samples of blood
hemolysis
destruction (lysis) of erythrocytes and the release of their hemoglobin into circulation
hemolytic disease of the newborn (HDN)
(also, erythroblastosis fetalis) disorder causing agglutination and hemolysis in an Rh+ fetus or newborn of an Rh− mother
Rh blood group
blood-type classification based on the presence or absence of the antigen Rh on the erythrocyte membrane surface
universal donor
individual with type O− blood
universal recipient
individual with type AB+ blood
1. The process in which antibodies attach to antigens, causing the formation of masses of linked cells, is called ________.
A) sensitization
B) coagulation
C) agglutination
D) hemolysis
C
2. People with ABO blood type O ________.
A) have both antigens A and B on their erythrocytes
B) lack both antigens A and B on their erythrocytes
C) have neither anti-A nor anti-B antibodies circulating in their blood plasma
D) are considered universal recipients
B
3. Hemolytic disease of the newborn is a risk during a subsequent pregnancy in which ________.
A) a type AB mother is carrying a type O fetus
B) a type O mother is carrying a type AB fetus
C) an Rh+ mother is carrying an Rh− fetus
D) an Rh− mother is carrying a second Rh+ fetus
D
1. Following a motor vehicle accident, a patient is rushed to the emergency department with multiple traumatic injuries, causing severe bleeding. The patient’s condition is critical, and there is no time for determining his blood type. What type of blood is transfused, and why?
In emergency situations, blood type O− will be infused until cross matching can be done. Blood type O− is called the universal donor blood because the erythrocytes have neither A nor B antigens on their surface, and the Rh factor is negative.
2. In preparation for a scheduled surgery, a patient visits the hospital lab for a blood draw. The technician collects a blood sample and performs a test to determine its type. She places a sample of the patient’s blood in two wells. To the first well she adds anti-A antibody. To the second she adds anti-B antibody. Both samples visibly agglutinate. Has the technician made an error, or is this a normal response? If normal, what blood type does this indicate?
The lab technician has not made an error. Blood type AB has both A and B surface antigens, and neither anti-A nor anti-B antibodies circulating in the plasma. When anti-A antibodies (added to the first well) contact A antigens on AB erythrocytes, they will cause agglutination. Similarly, when anti-B antibodies contact B antigens on AB erythrocytes, they will cause agglutination.