manufacturers for compatibility-testing is less sensitive than the reagent anti-RhO(D).
The microagglutinates consist of Rh-positive fetal cells coated with reagent anti-RhO(D)
reacting with the antiglobulin serum.
b. Agglutination in the microscopic phase of the DU test may not indicate a
massive fetomaternal hemorrhage, but may be caused by:
The patient being a weak DU.
(2) The reagent anti-RhO(D) slide or rapid tube test serum not being
standardized for close microscopic reading in the antiglobulin test.
(3) "Contamination" of the anti-RhO(D) reagent serum with a second weaker
antibody that is reacting with the patient's RBCs.
c. Confirmation of the hemorrhage is established by the acid-elution test of
Kliehauer-Betke. This test is performed on a postpartum blood smear of the mother.
d. If the diagnosis of a massive fetomaternal hemorrhage is confirmed, the
volume of the fetomaternal hemorrhage must be determined, in order to calculate the
number of vials of RhIG, to administer. Volume estimates are probably best determined
from the acid-elution test. One vial of RhIG is sufficient for 15 ml packed cells (30 ml of
fetal whole blood). Since the accuracy of the acid-elution test is poor (half to twice the
actual volume of the hemorrhage), it is preferable to administer a slight excess of RhIG.
A simple method described by Kliehauer for calculating the volume of the fetomaternal
hemorrhage gives an estimate that is equal in accuracy to more complicated formulas.
The volume of the fetomaternal hemorrhage can be calculated by multiplying the
percentage of fetal cells times 50. Since each dose of RhIG protects against
sensitization from approximately 30 ml of fetal blood, the volume of the fetomaternal
hemorrhage is divided by 30 and multiplied by 2. The two is a correction factor because
the Klliehauer estimate of fetomaternal hemorrhage may be as little as one half the
actual volume of the hemorrhage.
Counting of 2,000 cells in acid elution smear reveals 1.2 percent fetal
1.2 x 50 = 60 ml fetomaternal hemorrhage
60 x 2
2 x 2 = 4 vial of RhIG required
e. When multiple vials of RhIG are to be administered to the mother, base line