Cord red blood cells from an infant suspected of having hemolytic
disease of the newborn is most likely to be tested by which of the
following?
A. Passive hemagglutination test
B. Hemagglutination inhibition test
C. Nephelometry
D. Direct coombs test
A. Passive hemagglutination test
B. Hemagglutination inhibition test
C. Nephelometry
D. Direct coombs test
Ans. D.
The direct version of the Coombs test would be performed to determine if
the infant has maternal IgG (anti-Rh) already bound to the erythrocytes in the
cord Blood. IgG antibodies are relatively small. When they coat large particles
or cells, such as erythrocytes, they do not readily agglutinate them. In the
direct Coombs test, anti-immunoglobulin (antibody against the Fc region of
human IgG) is directly added to the infant's erythrocytes. The anti-immunoglobulin
(also known as Coombs reagent) spans the distance between cells to form an
agglutinating lattice that can be visualized in the test tube.
