Presentation on theme: "Identifying Antibodies"— Presentation transcript:
1Identifying Antibodies The Antibody PanelCLS 422Clinical Immunohematology I
2ObjectivesDiscuss clinical situations when it is appropriate to perform antibody identification.Define a panel of cells.Explain how the following factors aid in the interpretation of antibody panels:a. Cross-out techniqueb. Variation in strengths of reactionc. Phases of reactiond. Autocontrole. Red blood cell antigen typing
3ObjectivesList testing that can be performed to confirm the identification of antibodies.Identify the antibodies present, when given panel results.
4When is an antibody identification panel performed? When the antibody screen is positive.
5When to perform testThe panel red blood cells (RBCs) are tested against the patient’s serum or plasma in order to identify the unexpected antibody or antibodies present.May also test the panel cells against an eluate made from the patient’s RBCs when the patient has a positive DAT with IgG, in order to determine the identity of the antibody coating the RBCs.
6Identification Antibody screen – positive Run antibody panel to identify antibody (-ies).If original panel does not provide a clear-cut ID, test additional RBCs.Selected cellsAlternate methods
7Confirmation Rule of 3 and 3 Antigen type patient’s RBCs. Landsteiner’s Law!!!Rule of 3 and 3 - The probability that the reactions observed are due to a given antibody specificity and are not due to random chance. 3 antigen positive cells react with the serum; 3 antigen negative cells fail to react with the serum. This gives 95% confidence that the antibody ID is correct.In order to form an antibody, the patient’s RBCs should lack the antigen (type as antigen negative).
8The Panel Series of 8 to 20 Group O RBCs Various distribution of the most common RBC antigensSuspended in a preservative to protect antigen integrity for 2 -4 weeksPackaged with a lot-specific antigramDesigned for each specificity to have a unique pattern of positive and negative cells.
9AntigramThe panel is accompanied by an antigen profile sheet, which lists the antigens present on each cell, and provides a place to record results. The profile sheet is lot specific.
10Panel AntigramDonorCell numberDCcEeCwKkKpaKpbJsaJsbFyaFybJkaJkbLeaLebP1MNSsLuaLubXgaRZR11+R1wR12R2R23r’r4r’’r5rrK6rrFya7Ror8rr9R2r10R1R111PatientCellsWhich cell is homozygous for K antigen? 10 (It is somewhat unusual to have a K+k- cell on a panel since k is a high prevalence antigen.Which cell is heterozygous for C antigen? 4Which cell will react best with anti-Jka? 5, 6, 8, 9, 10 because they have homozygous antigen expressionWhich cell is probably from a Black donor? 1 or 8 because they are Fy (a-b-)Which donor is a secretor? 1, 2, 5, 6, 8, 9, 10 (positive for Leb)
11Auto ControlPatient’s serum/plasma tested against a suspension of patient’s RBCsOptionalEvaluate results in conjunction with patient historyAutoantibodyNewly forming alloantibodyIf patient has a positive DAT, auto control will be positiveThe auto control is not required by regulation.Some institutions will test the auto control in conjunction with the antibody screen or the panel. Some institutions opt not to test an auto control.A DAT may be tested in place of the auto control.
12Test Method Usually the same as was used for the antibody screen Must include incubation at 37oCMust include an AHG phase with reagent containing anti-IgGApplication of the indirect antiglobulin test.
14CellDCcEeCwKkKpaKpbJsasbFyaybkakbLaebP1MNSsuaLubXgaAHGCC+3+22+34567891011wAutoIf the antibody in the serum is directed against one of the antigens present on a panel cell, that cell should test positive.If the antibody is not directed against an antigen on the panel cell, the cell should give a negative reaction.
15Exclusion Begin with the RBCs that failed to react The antibody in the serum is not directed against the antigens on these RBCs, so we can eliminated these antibody specificitiesLook at alleles to avoid problems with dosage!Exclusion should be done using RBCs having homozygous antigen expression.Exceptions are low prevalence antigensDosage – An antibody may not react with a cell that has both alleles present, if the antibody is showing dosage. By using RBCs with homozygous antigen expression, you avoid eliminating an antibody showing dosage.Low prevalence antigens are K, Kpa, Jsa, and Lua.Since antibodies of the Kell system do not show dosage, it is not necessary to use homozygous cells in order to exclude antibodies to Kell antigens.A second exception to the “homozygous” rule is when anti-D is present is a patient’s serum. It may be difficult to find a cell that is D negative and has homozygous expression of C or E. In this situation ONLY, C and E may be excluded using a cell with heterozygous antigen expression (i.e. r’r for C and r”r for E)When needed, screen cells can be used for exclusions too!
16ExclusionCellDCcEeCwKkKpaKpbJsasbFyaybkakbLaebP1MNSsuaLubXgaAHGCC+3+22+34567891011wAutoCell 1 cannot be used for exclusion, as it reacted with the patient’s serum. The specificity of the antibody should match one of the antigens present on Cell 1.Cell 2 can be used to exclude: D, C, e, Cw, k, Kpb, Jsb, Fyb, Jkb, Leb, P1, s, Lub, and Xga.Cell 3 excludes: c, E, Fya, and M.Cell 4 excludes: Jsa, Jka, and N.Cell 5 could be used for exclusion, but in this case does not exclude any new specificities.Cell 6 excludes Lea.Cell 7 cannot be used for exclusion because it yielded a positive result.Cell 8 can be used to exclude Lua.Cell 9 excludes S.Cell 10 cannot be used for exclusion because it reacted with the serum.Cell 11 could be used for exclusion, but in this case, does not exclude any additional specificities.
17InclusionOf the antibody specificities that have not been excluded, match the pattern of positive and negative reactions with the pattern of antigen positive and antigen negative cells.There must be an explanation for each positive reaction seen.
18InclusionCellDCcEeCwKkKpaKpbJsasbFyaybkakbLaebP1MNSsuaLubXgaAHGCC+3+22+34567891011wAutoOnly K and Kpa remain. The pattern of reactivity (inclusion) matches anti-K. Kpa has NOT been eliminated, i.e. we cannot say that anti- Kpa is not present because none of these panel cells were Kpa positive.
19Other Points to Consider In what phase(s) of testing is the antibody reactive?May give clue as to antibody identity and clinical significance.Is the strength of reaction the same for each cell that reacts, or is there variation in strength?Dosage, antigen variability, or multiple antibodies.Is the antibody reacting only with “homozygous” cells of a certain specificity?Weak antibody showing dosage.Did the autologous control react?Autoantibody or newly forming alloantibody.
20Probability Rule of 3 and 3 For each antibody specificity, are there 3 antigen positive cells that reacted and 3 antigen negative cells that did not react?May use screen cells in addition to panel cells to fill this ruleCells do not need to have homozygous antigen expression to fill this rule
21The Rule of 3 and 3CellDCcEeCwKkKpaKpbJsasbFyaybkakbLaebP1MNSsuaLubXgaAHGCC+3+22+34567891011wAutoCells 1, 7 and 10 are K positive and gave a positive reaction. Cells 2-6, 8, 9, and 11 are K negative and they did not react. We can be 95% confident that anti-K is present in this specimen.
22Antigen Typing Confirms the antibody identification LANDSTEINER’S LAWTest patient’s RBCs (unknown antigen) against appropriate anti-sera (known antibody)Results should benegativeRun positive and negative controls for anti-seraA positive DAT or recent transfusion may invalidate the typing resultsLandsteiner’s Law states that a person should not make an antibody against an antigen that their cell possesses.The positive control should be a cell with a single dose of the antigen (heterozygous) in order to prove sensitivity (the reagent is potent enough to detect even small amounts of the antigen).Many of the typing anti-sera rely on an IAT procedure.
23Selecting Controls for Antigen Typing CellDCcEeCwKkKpaKpbJsasbFyaybkakbLaebP1MNSsuaLubXgaAHGCC+3+22+34567891011wAutoFor anti-K typing serum, cells 1, 7 or 10 could serve as a positive control.Cells 2 -6 , 8, 9, or 11 could serve as a negative control.
24Value of Patient History The following additional information may assist in determining the identity of the antibody:History of antibodiesTransfusion, transplant, pregnancy (how many and how long ago)MedicationsDiagnosisEthnicity
25ReportingPanel results are reported as “anti-” and then the specificityAnti-KIf specificity cannot be determined at this point, additional testing must be performed