Special Blood Tests

Determination of Hemolytic Disease of the Newborn
If a woman has Rh negative blood and husband is Rh positive, generally the child will inherit the father’s dominant Rh positive factor. Most Rh problems arise during the second or third pregnancy. This disorder is caused by the presence of an antigen in the infant’s blood, which is not present in the mother’s blood. Corresponding antibodies are developed by the mother against this antigen. These antibodies destroy the baby’s red blood cells. If antibodies are high in number, then the fetus may die or be expelled before the normal gestation period. If antibodies are low in number, then the baby is born alive with hemolytic jaundice. Since the red blood cells are destroyed, it causes oxygen starvation as red blood cells carry oxygen. In severe cases, the infant dies unless complete replacement of blood is done immediately after birth. The procedure is called exchange transfusion.
The infant’s blood tests and other findings show the following:

Abnormal RBCs.
Increased Reticulocyte count.
Platelets will be normal or decreased.
Low hemoglobin at birth and further decreases rapidly as the disease progresses.
Direct antiglobin (coomb’s) test on the baby’s red cells is +ve.
Umbilical cord blood – bilirubin is about 3.0 mg/dl and rises fast and may go up to 40 to 50 mg/dl. Bilirubin above 20 mg/dl can cause severe brain damage called Karnicterus.
Even kidney damage/failure and cardiac failure may result.
Hepatosplenomegaly (enlargement of liver and spleen).

Determination of Possible Blood Group of A Child

Blood Group	Father	Mother	Possible Group Of Child
Blood Group	A	A	A
	A	O	A or O
	A B	B	AB or A or B
	A	B	A or B or O or AB

Indirect Antiglobulin (Coomb’s) Test
This test is performed to detect presence of Rh antibodies or other antibodies in patient’s serum, in the following cases:

To check whether an Rh negative woman (married to Rh positive husband) has developed anti Rh antibodies.
Anti D may be produced in the blood of any Rh negative person by exposure to D antigen by
- Transfusion of Rh positive blood.
- Pregnancy, if the infant is Rh positive (if father is Rh positive).
- Abortion of Rh positive fetus.

Direct Antiglobulin (Coomb’s) Test
This test is performed to detect anti D antibody or other antibodies attached to red blood cells in the blood stream. It is done in the following conditions.

When there is Rh +ve baby in the womb of a Rh –ve woman, to defect hemolytic anemia (described in hemolytic disease of newborn).
Transfusion reactions.
Drug induced red cell sensitization.
Autoimmune hemolytic anemia.

Compatibility or Cross–matching Test
This is done before transfusion of blood to a patient of the cross–matching as non–compatible blood should never be transfused. Minor cross match results are also important but in an emergency one can use blood with minor incompatibility.

Users' Comments