Rh FACTOR
Rh factor is an antigen present in RBC. This antigen was discovered by Landsteiner and Wiener. It was first discovered in Rhesus monkey and hence the name ‘Rh factor’. There are many Rh antigens but only the D antigen is more antigenic in human. The persons having D antigen are called ‘Rh positive’ and those without D antigen are called ‘Rh negative’. Among Indian population, 85% of people are Rh positive and 15% are Rh negative. Percentage of Rh positive people is more among black people.
Rh group system is different from ABO
group system because, the antigen D does not have corresponding natural antibody
(anti-D). However, if Rh positive blood is transfused to a Rh negative person
anti-D is developed in that person. On the other hand, there is no risk of complications
if the Rh positive person receives Rh negative blood.
INHERITANCE OF Rh
ANTIGEN
Rhesus factor is an inherited dominant
factor. It may be homozygous Rhesus positive with DD or heterozygous Rhesus
positive with Dd. Rhesus negative occurs only with complete absence of D (i.e.
with homozygous dd).
TRANSFUSION REACTIONS
DUE TO
Rh INCOMPATIBILITY
When a Rh negative person receives Rh
positive blood for the first time, he is not affected much, since
the reactions do not occur
immediately. But, the Rh antibodies develop within one month. The transfused
RBCs, which are still present in the
recipient’s blood, are agglutinated. These agglutinated cells are lysed by macrophages.
So, a delayed transfusion reaction occurs. But, it is usually mild and does not
affect the recipient. However, antibodies developed in the recipient remain in
the body forever. So, when this person receives Rh positive blood for the second
time, the donor RBCs are agglutinated and severe transfusion reactions occur
immediately. These reactions are similar to the reactions of ABO
incompatibility.
HEMOLYTIC DISEASE OF
FETUS AND NEWBORN – ERYTHROBLASTOSIS FETALIS
Hemolytic disease is the disease in
fetus and newborn, characterized by abnormal hemolysis of RBCs. It is due to Rh
incompatibility, i.e. the difference between the Rh blood group of the mother
and baby. Hemolytic disease leads to erythroblastosis fetalis. Erythroblastosis
fetalis is a disorder in fetus,
characterized by the presence of
erythroblasts in blood. When a mother is Rh negative and fetus is Rh
positive (the Rh factor being inherited
from the father), usually the first child escapes the complications
of Rh incompatibility.
This is because the Rh antigen cannot pass from fetal blood into the mother’s
blood through the placental
barrier.
However, at the time of parturition (delivery of the child), the Rh antigen
from fetal blood may leak into mother’s blood because of placental detachment. During postpartum
period, i.e. within a month after delivery, the mother develops Rh antibody in
her blood. When the mother conceives for the second time and if the fetus
happens to be Rh positive again, the Rh antibody from mother’s blood crosses
placental barrier and enters the fetal blood. Thus, the Rh antigen cannot
cross the placental barrier, whereas
Rh antibody can cross it. Rh antibody which enters the fetus causes
agglutination of fetal RBCs resulting
in hemolysis. Severe hemolysis in the fetus causes jaundice. To
compensate the hemolysis of more and
more number of RBCs, there is rapid production of RBCs, not only from bone
marrow, but also from spleen and liver. Now, many large and immature cells in
proerythroblastic stage are released into circulation. Because of this, the
disease is called erythroblastosis fetalis.
Ultimately due to excessive hemolysis
severe complications develop, viz.
1. Severe anemia
2. Hydrops fetalis
3. Kernicterus.
0 Comments