(2) A great many variations of A reactivity have been identified. In general,
these follow a spectrum of declining numbers of A antigen sites, and increasing strength
of H reactivity. Variants of A differ from one another in the presence or absence of anti-A1
or anti-A activity in the serum; in the presence or absence of salivary A substance; and
in the degree to which they are agglutinated by the inseparable, or cross-reacting, anti-
A,B serum or by anti-A serums boosted by specific immunization. Different workers
employ slightly differing terminology to describe variants.
(3) The problem of selecting appropriate blood for transfusion of a patient
with variant A antigens or antibodies is addressed in paragraph 1-47 of Subcourse
c. Weak Subgroups of B. No allele analogous to A2 has been found for B.
There are, however, very rare genes that affect the expression of red blood cells and
salivary B in manners somewhat comparable to the effect of Ax, Am, and other variants
of A activity.
d. The Bombay Phenotype. Individuals homozygous for the rare gene h have
red cells devoid of A, B, or H antigens. On initial testing the cells appear to be from
group O, and the phenotype is called Oh. The Oh phenotype is popularly called
"Bombay" because it was first discovered in Bombay and seems to occur more often in
India than elsewhere. In routine testing, Oh bloods may appear to be group O since the
red cells are not agglutinated by anti-A or anti-B and the serum agglutinates both A and
B red cells. Because Oh persons lack H substance on their red cells, their serum
contains anti-H that is as strong as the anti-A and anti-B.
2-14. SPECIAL PROCEDURES-TEST FOR HEMOLYSINS
If whole blood is to be given to a recipient of another blood type (group O to A or
B; group A to AB), the donor blood must be free of hemolysins. It is far preferable not to
give whole blood; give red blood cells instead.
a. STEP 1: Use complement-containing serum, not plasma or aged or
b. STEP 2: Place two drops of serum in each of two tubes labeled A and B.
c. STEP 3: Add two drops of 2 to 5 percent saline suspension of washed fresh A1
cells to tube A and 2 drops of B cells to tube B.
Use of a weaker cell suspension or larger amounts of serum will increase
incidence of hemolytic activity.
d. STEP 4: Mix gently and incubate at 37C for 10 to 15 minutes.