Antibody panels

Most antibody panels in the exam should be a fairly straightforward antibody present. It's possible to get an elution; panels from adsorptions will be rarer because it takes more time to go through these (and if there is one it will be equally straightforward).

Recall:

IAT = indirect antiglobulin test. This is mixing the patient's plasma (which contains a potential antibody) onto a panel of known, typed red cells and the additional of anti-human globulin (AHG), and recording the agglutination level. This is typically done at 37C.

LISS = low ionic strength saline. This is used to cause red cells to repel each other.

If you have saved some of your panels from the transfusion courses (ETM/ITM/one week revision course) it will be useful to revisit these.

Some guidelines in interpreting panels:

1. Check the details of the patient at the top (if available).

2. Make sure you do the ABO grouping, and check all the positive and negative controls to ensure they are working correctly. If they are not, the antibody panel is not valid.

3. Single alloantibodies will be easy to detect. Confirmation of a positive antibody requires two positive homozygous cells. Enzyme reactions are sometimes provided to clarify the result given in the IAT, and may help to distinguish multiple antibodies (although a more extensive panel may be required). Enzymes such as papain remove sialic acid residues on red cells.

Enzyme reactions will be enhanced in:

• Rh groups
• Kell group (sometimes)
• Kidd group (sometimes)

Enzyme will destroy reactions in:

• Duffy group (but not Fy3)
• Kell group (sometimes)
• MNSs group

4. A heterozygous cell may diminish the antibody reaction as they will have half the antigens available. For example - a cell within a panel which is Jka+/b- will have two Jka groups and no Jkb groups: and so any Jka reaction might be stronger. A cell which is Jka+/b+ will have one Jka group and one Jkb group, which might result in a weaker positive reaction. If there is an anti-Jka antibody in one cell the reaction might be stronger in the homozygous cell than the heterozygous cell (so don't just assume that it's two separate antibodies). Generally summation of reaction occurs most commonly in the Jka/b and S/s antigens.

5. You should not need to perform exclusions on the antibody panels unless specifically requested (very unlikely to happen). It will however be important to write on the answer booklet that you would proceed to request these. The rule for exclusions is for them to be twice excluded on homozygous cells.

6. anti-M antibodies are only clinically significant if they are positive at 37C. If the antibody is only done with saline this will be marked at room temperature and this should be repeated at a 'strict 37C' (i.e. all steps of sample processing should be done at 37C - not just the antibody panel). If the antibody is negative at 37C then you can select red cell units which are 'unselected for M'.

For some practice panels please review the transfusion questions page.