2-28. GENERAL CONSIDERATIONS IN Rh-TESTING
a. The following problems may cause false positive results in Rh-testing:
(1) Serum-suspended cells from patients with abnormal serum proteins may
form rouleaux which resemble agglutination. This will occur in both test and control
tube, since the same suspension is in both. To resolve, use a well-washed saline
suspension and test with saline-agglutinating reagents.
(2) Polyagglutinable cells may be agglutinated by any human protein
reagent, because the antibodies that agglutinate these surface-altered cells are present
in all adult serums. All reagent Rh antibodies derive from human serum. The control
tube may not agglutinate if bovine albumin is used as the protein. Except for group AB
cells, this situation would become obvious when cell and serum ABO tests disagree.
Both ABO and Rh discrepancies should be resolved before transfusing the patient. In
an emergency, group O, Rh-negative packed cells should be given. Polyagglutinable
cells cannot be used as donor cells.
(3) Contaminating antibody with specificity other than that indicated by the
label could cause agglutination. Agglutinating antibodies are rare with well-
standardized, licensed serum, but antiglobulin-active antibodies are not uncommon.
Quality assurance techniques might not detect the problem if the cell used as the
negative control were also negative for the antigen recognized by the contaminating
antibody. Many blood banks prefer to perform duplicate tests, with different lots of
antiserum, so that discrepant results of this sort can be detected.
b. The following problems may cause false negative results in Rh-testing:
(1) If an antibody recognizes only a compound antigen, it will not react with
cells which carry the individual specificities as separate gene products. For example: A
supposed anti-hr"(e) serum that was anti-hr (f or ce), would give negative results against
R1R2 (CDe/cDE) cells, or any other cells on which the hr"(e) antigen was part of a gene
product that did not include the compound antigen. This problem is difficult to detect in
testing individual samples, unless complete phenotypic testing allows one to make an
accurate estimate of probable genotype. Well-defined quality assurance procedures in
antibody processing should obviate the problem.
(2) Cells with variant antigens like Cw or ces may fail to react with standard
antiserums. This is especially difficult to detect because the results of duplicate testing
will be similar. Discrepant results in family studies are the usual clue that further
investigation is needed. Sometimes blood "negative" for an antigen elicits antibody
which reacts with both the variant and the normal antigen, and the variant is discovered
in investigating the immunization.