2-10. CELL AND SERUM ACTIVITY
a. Background. Serum antibodies are not directly determined by gene activity,
but are important phenotypic characteristics in the ABO system. Under most
circumstances, most individuals possess antibodies directed against the ABH antigens
absent from their own cells. This predictable complementary relationship is the basis
for using both serum and cell tests in blood grouping. The cells are observed for the
presence or absence of agglutination by known anti-A and anti-B. Cell-testing is
sometimes called direct-or forward-testing. The unknown serum is tested against
known A and B cells, sometimes called reverse- or back-testing. Since the genetically
determined cellular antigens are rarely altered by environmental modification, cell-
testing alone is more reliable than serum-testing alone. Both should be routinely
performed, partly because the tests serve to verify each other, and partly because
investigation of discrepancies usually reveals a medically or serologically significant
etiology. Table 2-5 shows the phenotypic products that develop when different genes
from these independent but interacting systems are present.
Table 2-5. Red blood cell and salivary antigens determined by ABO, Hh, sese, and lele
genes.
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