Haemolytic Disease of the Newborn due to ABO incompatibility

Forget about the overpublicized HDN due to Rhesus incompatibility and read about this one; 

It is an immune haemolytic anaemia which causes an infant to be born anaemic and jaundiced.
ABO HDN can occur when a group O mother with a high titre of immune IgG anti-A and anti-B (usually >1:64) in her serum becomes pregnant with a group A or group B infant.
IgG anti-A and anti-B cross the placenta and enter the foetal circulation causing destruction of foetal red cells.
Group B infants are often more severely affected than group A infants.

INVESTIGATIONS
1. ABO cell grouping of the infant using washed cord cells. When the infant is group A or group B carry out the following:

2. Maternal-infant ABO blood group incompatibility test as follows:
(i) pipette 2 volumes of fresh serum from the mother into a tube.
(ii) add 1 volume of infant's washed 5% cell suspension and mix.
(iii) incubate at 37 degrees Celsius for 15 minutes. Centrifuge at slow speed (150 rpm) for 1 minute.
(iv) examine the tube for haemolysis.
* Lysis of the red cells indicates ABO HDN.

3. Direct Coomb's Test (DCT) on the infant's red cells to check whether they have been coated with IgG antibody.

4. Check haemoglobin.

5. Check serum bilirubin of the infant.

6. Romanowsky-stained thin film--this shows spherocytosis which may be marked, polychromasia (due to reticulocytosis) and nucleated red cells.

NOTE:
*ABO HDN is rarely sufficiently severe to require exchange transfusion. In a situation in which it is indicated, group O blood (of the same Rhesus group as the infant) should be selected and cross matched with mother's serum.
*In contrast to Rhesus HDN, ABO HDN may occur in the first pregnancy and may not affect subsequent pregnancies depending on the ABO group of the infant.