47 Antibody Identification, Exclusions and Confirmations…
The following information provides guidance to students on the antibody identification process step-by-step.
- Review patient history (age, transfusions, pregnancies, ABO and Rh group) and antibody screening results (file)
- Review panel results
- Initial Impressions:
- What phase(s) is/are the antibodies reacting in (warm/IgG vs cold/IgM)?
- Are ALL rbc’s in panel reactive? (suggests antibody to high incidence antigen)
- Are all reactions of similar strength? If not, think “multiple antibodies” or “dosage” (Rh, MNS, Duffy and Kidd blood groups)
- Is the auto control reactive (positive) or nonreactive (negative)?
- Exclusions (“ruling out” antibodies)
- Look at all negative cells. If an “antigen” is present on the cell and the plasma “did not” react with the cell, the presence of the “corresponding” antibody may be excluded, taking into consideration dosage and antigen variations.
- Cross out those antigens present on negative cells using the “rules” of exclusion:
- To exclude antibodies capable of dosage (Rh, MNS, Duffy and Kidd blood groups) a homozygous “double dose” antigen positive cell is required.
- To exclude “D”, “K” and “P1” 3 “single dose” cells can be used for exclusion.. “D” because it is unknown if it is single or double dose(only Rh MPG); for the “K” because it is too hard to find a double dose cell (if you do find a double dose cell you may use it to exclude); and for the “P1” because of the potential antigen variation on the cells.
- Exclude antigens “without” alleles (f, Le, Xga) exclude based on 1 positive cell
- Exclude rare antibodies : Anti- Cw, -V,- Kpa, -Jsa, -Lua , based on 1 positive cell however, routine exclusion is not required unless an antibody directed against a low frequency Ag is suspected (ie the panel cell carrying the Ag is positive and there are no other antibodies or explanations for the positive result)
- Evaluate the RCs that were reactive with the patient’s plasma and the potential antibodies that remain after exclusion. What are the possibilities?
- Is there a “perfect fit” or “direct hit” pattern?
- Can reaction variations or phase variations be accounted for?
- Have you excluded ALL clinically significant antibodies? If not, what can you do to exclude them (ie select cells/panels)?
- Setting up select panels: Use the rules of exclusion to select cells and finish excluding antibodies
- What other “techniques” can be used to confirm/exclude antibodies?
- antigen testing
- patient phenotyping
- enzyme panels
- adsorptions
- neutralization
- Confirmation!!
- Does patient lack antigen to the corresponding antibody (if auto is negative)?
- 3+3 rule based on statistical probability: Once the identity of the antibody or antibodies, is determined, final confirmation is based on a minimum of 3 antigen positive RC’s that react with the antibody (patient’s plasma) and a minimum of 3 antigen negative cells that do NOT react with the antibody (patient’s plasma). When multiple antibodies are present: you must use the 3+3 rule where the cells that are used to confirm the presence of antibodies may be positive for only one of the corresponding antigens (at a time). You will require two more positives for each individual antigen and a negative for all antigens.
Example: You have identified an anti-K and an anti-E in the patient’s serum. You must review all cells (screening, panels and select panels) and find the following for statistical confirmation:
- 3 K+, E- cells that are positive
- 3E+, K- cells that are positive
- 3 K-, E- cells that are negative
- Finding compatible units:
- When patient has antibodies you MUST perform a serological crossmatch (by antiglobulin testing). Immediate spin crossmatches and computer crossmatches can ONLY be used when the patient has NEVER had a history of or has antibodies!
- Compatible units MUST be antigen tested before issuing and must be negative for the antigen to the corresponding antibody in the patient
- To find/ test a sufficient number of units?
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- When patient has antibodies you MUST perform a serological crossmatch (by antiglobulin testing). Immediate spin crossmatches and computer crossmatches can ONLY be used when the patient has NEVER had a history of or has antibodies!
- Compatible units MUST be antigen tested before issuing and must be negative for the antigen to the corresponding antibody in the patient
- To find/ test a sufficient number of units? Finding compatible units:
- Use the “incidence” of the antigen (s) to calculate:
Example: Patient has anti-K, require 2 compatible units
Need to know the negative frequency of the Ag (9% have “K” Ag therefore 91% do not have “K” Ag-negative frequency is 0.91)
Need 2 units. Divide the number of units required by the negative frequency: 2/.91=2.2 (3) units (approximately-based on the statistics) need to be screened to get 2 compatible units