Blood Bank and Pregnancy

Blood bank and pregnancy:
As outlined earlier, blood bank can be an important department for expecting mothers. Other than the D test, there are a few other important things to be aware of.

Cord blood:
Cord blood is collected from every newborn. ABO, Rh, and DAT are tested if one or more of the following exists:

1. Rh-negative mother
2. Group O mother
3. Mother has an antibody that could cause HDN
4. Doctor request
5. Unknown results for the mother (ABO, Rh, unknown antibody)

Rhogam (RhIg):
Rh Immune globulin, known by its trade name Rhogam or simply RhIg is an important medication. In Rh-negative mothers with Rh-positive newborns it is used to neutralize Rh+ RBCs. RhIg is passive anti-D and works by binding to the Rh+ RBCs and when bound are removed by the spleen before the mother’s immune system makes anti-D. 1mL (300 micrograms) neutralizes 15mL of packed red cells or 30mL of whole blood.

Fetal Screen:
A fetal screen can be run to determine if a mother needs to be administered multiple doses of RhIg. It’s run by combining maternal RBCs and reagent anti-D. The anti-D will bind to any fetal Rh-positive RBCs. Excess anti-D is then washed off and an indicator is added which will cause rosettes to form if positive. If 3-5 rosettes are found, this is a positive test and a Kleihauer-Betke test should be run.

Kleihauer-Betke test:
The Kleihauer-Betke test is used to determine the amount of feto-maternal hemorrhage (FMH), the amount of fetal blood that has crossed into the mother. The test uses an acid elution method that removes adult hemoglobin but not fetal hemoglobin. The cells are then stained which leaves fetal red cells pink and maternal red cells as a light gray-pink cell referred to as “ghost” cells.

The equation used to calculate percent FMH is as follows:
volume FMH = # of pink fetal cells / total cells x 5000

This calculation can then be used to calculate the vials of RhIg needed.

For example if you found 12 fetal cells in a total of 1500 cells you would get 40mL FMH. You then divide 40mL by 30mL (30mL is a constant) and get the value 1.33. You then round this number, if it is .5 or higher round up and .49 or lower round down. In this case we would round down to 1. Then one vial is added for safety giving a total of two vials for this patient. Hypothetically, if the patient had a value of 1.5, it would be rounded to 2 and then a safety vial added giving a total of three vials.

Neonate with anemia or in need of a transfusion:
For compatibility testing for an infant less than 4 months old, antibody detection can be performed using maternal or infant plasma. The infant’s immune system is not well developed yet, so maternal or infant plasma can be used to detect unexpected non-ABO antibodies.