Screening

Grouping

Screening

ANTIBODY IDENTIFICATION

(INDIRECT ANTI-HUMAN GLOBULIN TEST)

When an antibody is detected in the patient's serum this is identified using panels of red cells of known phenotype. There is a defined procedure for the identification of antibodies. Read the results of the gel cards and record on the panel sheet on which the donor's phenotype is shown.

1. When no positive reaction was observed, exclude antigens with a cross for homozygotes and a single line for heterozygotes.

2. Examine the antigens that have not been excluded to see if any account for all the reactions observed and that the reaction is in the phases that are usual for an antibody of that specificity.

3. Further investigation with cells of known phenotype (negative for an antigen where there is an identified reaction, but positive for an antigen to be excluded), with composite panels or by typing the patient, may be required.

The pattern of reactivity seen with a panel could arise by chance and there is a requirement that the result be significant at at least the 95% confidence level. Three antigen positive reactive cells and three antigen negative unreactive cells are required.

In Rh negative individuals anti-D is the most common antibody be accompanied by anti-C, anti-Kell or anti-Fya. These can be in combination with antibodies that are rarely clinically significant - anti-P1 or anti-Lewis a or b (alone or together).
In Rh positive individuals the most frequently detected antibodies are anti-E, anti-Kell and anti-Fya, less frequently anti-cE, anti-c. These can also be in combination with antibodies that are rarely clinically significant - anti-P1 or anti-Lewis a or b (alone or together).

Following a positive screen the serum is reacted with a panel of cells. It is essential that antibodies are quickly and accurately identified in order that donor blood may be provided. When a pattern is not clear or several specificities have not been excluded, a second panel is usually set up (to provide more information for exclusions).