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Antibody identification and its importance in blood transfusion

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  • Antibody identification and its importance in blood transfusion

    أبغى موضوع عن Antibody identification

    وأهميته في عملية blood transfusion

  • #2

    14.9 Antibody identification

    When an alloantibody is detected in the screening procedure, the specificity should be determined and its likely clinical significance assessed. It is essential to determine the specificity of all clinically significant antibodies present. It is important to employ a systematic approach to antibody exclusion in the process of antibody identification. Several reagent red cell panels may be needed to identify some combinations of antibodies.

    14.9.1 Principles of antibody identification

    The patient's serum or plasma should be tested by an appropriate technique against an identification panel of reagent red cells. As a starting point, the technique by which the antibody was detected during screening should be used. Inclusion of the patient's own red cells may be helpful, for example, in the recognition of an antibody directed against a high frequency antigen or the presence of an autoantibody.

    The specificity of the antibody should only be assigned when it is reactive with at least two examples of reagent red cells carrying the antigen and non-reactive with at least two examples of reagent red cells lacking the antigen. Note that, wherever possible, the presence of anti-Jka, -Jkb, -S, -s, -Fya, and -Fyb should be excluded using red cells having homozygous expressions of the relevant antigen.

    A weak anti-D control serum or reagent (containing anti-D at a level of approximately or less than 0.1 IU/mL) should be used on a regular basis to assure the efficacy of the whole test procedure, including antigen expression on screening or panel cells.

    When one antibody specificity has been identified, it is essential that the presence of additional clinically significant antibodies has not been missed. Multiple antibodies can only be confirmed by choosing cells antigen negative for the recognized specificity, but positive for other antigens to which clinically significant antibodies may arise. Knowing the phenotypes of the patient can aid in cell selection for the identification and exclusion process. The requirements detailed above should be met for each antibody detected but in some circumstances this may not be possible.

    The use of a panel of enzyme (e.g. papain) treated cells is strongly recommended for antibody identification, particularly when an antibody weakly reactive by the antiglobulin technique, or a mixture of antibodies, is present. The use of monospecific antiglobulin reagents in place of polyspecific reagent is beneficial when determining the presence of IgG antibodies in serum samples containing complement-binding antibodies. The use of room temperature saline techniques may also be helpful.

    14.9.2 Reagent red cells for use in antibody identification

    See Section 12.2.3 for details.

    If the patient is group A, B or AB and all reagent cells react with the test plasma, it may be useful to include cells of the same ABO group as the patient to exclude the possible presence of anti-HI.

    When the phenotypes of the patient are known, it is not necessary to look for any specificity where the patient is positive for the antigen. Where the patient is negative there should be at least two examples of cells with phenotypes lacking, and at least two examples of phenotypes carrying, expression of the corresponding antigen. The panel should be able to resolve as many likely antibody mixtures as possible.

    14.9.3 Red cell phenotyping in antibody identification

    When an antibody has been identified, the patient's red cells should be phenotyped using a reagent of the same specificity as the assigned specificity. Suitable controls should be used, i.e. antigen positive (from a heterozygote) and antigen negative.

    The patient's red cells, as determined during phenotyping, will normally be expected to lack the antigen(s) corresponding to the antibody specificity (specificities) assigned. If this is not the case:

    (a) the antibody may be an autoantibody (in which case the patient's cells will normally be DAT positive), and/or

    (b) if an antiglobulin or potentiated test method has been used, the patient's cells may be coated with globulin components (in which case the cells will be DAT positive)

    (c) the assignation of antibody specificity may be incorrect

    (d) the patient may have been recently transfused.

    The incorporation of a reagent control or AB serum control used by the same technique as the phenotyping reagent is recommended, unless the reagent is known to contain unpotentiated IgM antibody. A positive result in this control test will invalidate the phenotyping test results.

    When red cells taken from a blood donation unit are found to be positive in an antiglobulin crossmatch against patient's plasma, but no activity is detected in the plasma against red cells in an identification panel, it is likely that either:

    (a) the plasma contains an antibody to a low frequency antigen

    (b) the red cells in the donation are DAT positive

    (c) blood of the wrong ABO group has been selected for crossmatching.

    14.9.4 Extended red cell phenotyping

    It may be useful to perform extended red cell phenotyping to identify the potential antibodies that could be produced. This may not be possible to determine if the patient has been recently transfused. The following antigens should be tested for:

    C, c, D, E, e, M, N, S, s, K, k, Fya, Fyb, Jka, Jkb.

    14.9.5 Investigation of a broadly reacting plasma sample

    If all cells are positive, with reactions of equal strength:

    (a) An antibody to a high incidence antigen should be considered. The use of an enzyme (e.g. papain) treated panel is particularly useful as reactivity or non-reactivity of the test plasma may exclude certain specificities immediately, and save time and the unnecessary use of rare typing reagents.

    (b) The cells of the patient should be typed for as many high incidence antigens as possible and, if a negative is found, cells lacking that antigen should be matched against the patient's plasma. Where possible the antigen negative cells should include antigens that the patient lacks in order to exclude the presence of further, underlying, alloantibodies.

    If all cells are positive with varying degrees of strength:

    (a) When cells give different strength reactions and a mixture of antibodies cannot be confirmed antibodies to Ch, Rg, Csa, Kna / McCa (CR1-related) should be considered. Ch and Rg are antigens which reside on the C4d component of the complement protein C4 and the serological activity in IAT tests is due to the small amount of C4 adsorbed on to the surface of the cells in vivo. Coating reagent red cells with C4 in vitro in a low ionic strength medium enhances the serological reactivity of anti-Ch and anti-Rg. Plasma inhibition may also be used to confirm Ch and Rg specificities but dilution of the test plasma may be needed for complete inhibition to be observed.

    (b) Because of the heterogeneity of the CR1 protein not all examples of Kna-related antibodies have the same specificity. Therefore, the cells of different antibody makers may not be mutually compatible.

    Use of an extended range of enzyme (trypsin or chymotrypsin) treated and chemically (AET or DTT) modified cells can aid in the identification process if the specificity cannot be determined or is in doubt. Reactivity or non-reactivity of the test plasma may indicate a specificity within a certain blood group system.

    An eluate prepared from group O, antigen matched, cells and sensitized with antibody from the test plasma, may be helpful in antibody identification. The eluate will isolate any antibody (present in the test plasma) to a high incidence antigen and will enable the matching of rare phenotype cells, including null phenotype cells, of any ABO group.

    In a complex mixture of antibodies individual antibodies can be isolated by adsorption of one antibody on to red cells positive for the corresponding antigen and lacking the antigens for the other antibodies. An eluate may be prepared from the first aliquot of cells to confirm the specificity of the adsorbed antibody. Both the aliquots of absorbed sera and eluates can be tested for individual specificities. This procedure is useful when there are insufficient fully typed reagent panel cells available to detect each specificity individually in the raw serum.

    References

    1. Department of Health, The Caldicott Committee, Report on the Review of Patient-Identifiable Information. December 1997 available at www.dh.gov.uk.

    2. British Committee for Standards in Haematology (2004) 'Guidelines for compatibility procedures in blood transfusion laboratories', Transfusion Medicine, 14, pp59–73.

    3. Stainsby, D., MacLennan, S. and Hamilton, P.J. (2000) 'Management of massive blood loss: a template guideline', British Journal of Anaesthesia, 85(3), pp487–91.
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    • #3
      كفيت و وفيت اخوى تسلم السنهورى
      ومما ذادنى شرفا وتيها وكدت باخمصى اطاء الثريا دخولى تحت قولك يا عبادى وان صيرت احمد لى نبيا

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      • #4
        موضوع جميل وكفيت ذي ما قال جيفارا

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