15.5 Donor and patient testing
HLA Class I typed platelets should normally be provided for refractory patients on the basis a lack of mismatched Class I antigens. In the absence of a zero mismatched donor, a compatible donor can be selected on the basis of a lack of antigens or alleles corresponding to the antibody specifities identified in the patient. Where a patient's antibodies have not been characterised a crossmatch can be performed.
The most common cause of immunological refractoriness to random donor platelet transfusion is the presence of HLA-specific antibodies in the patient receiving platelet transfusion. The management of this group of patients may involve the provision of HLA-compatible platelets and or crossmatch-negative donors.
There are several crossmatch techniques for the detection of donor reactive antibodies that may involve the use of donor lymphocytes or donor platelets. The basic principle is the same for most of the techniques in that serum or plasma from the patient is incubated with donor cells and reactivity is detected by flow cytometry or cytotoxicity. Platelets from donors negative in the crossmatch testing may be used for transfusion of the patient whose serum has been crossmatched.
Potential HSC donors are typed for both HLA Class I and Class II for registration on one of the national donor panels.
Transfusion Associate Graft versus Host Disease (TAGvHD) can be a consequence of using immunocompetent blood products from donors that share HLA alleles with the patient, particularly where the donor carries no mismatched alleles.
HLA and/or granulocyte specific antibodies present in donor plasma have been implicated in nearly 90% of TRALI cases (patient leucocyte antibody or inter-donor reactions in pooled products have also been reported as causes of TRALI). The identification of leucocyte-specific antibodies in implicated donors provides support for the diagnosis of TRALI, which has similar features to acute respiratory distress syndrome (ARDS).
15.5.1 Apheresis platelet donors
All potential plateletpheresis donors used for the provision of HLA selected platelets should be typed for the HLA-A, -B and Cw. If serological typing is used the minimum level of typing should be for the HLA Class I specificities listed in Table 15.2. Resolution to the level of broad antigen group, shown in brackets, is acceptable. For all donors HLA-Bw4 or -Bw6 should be assigned.
If DNA-based typing is performed on donors a typing strategy should be employed that allows for HLA alleles to be defined to at least the two-digit level of resolution. Typing should also be capable of determining the presence of the Bw4 and Bw6 epitopes encoded by the HLA-B alleles and Bw4 for HLA-A.
Each donor should be HLA typed twice using samples collected on separate occasions, such that only if the second test confirms the first should the donor provide platelets for clinical use.
15.5.2 Haemopoietic stem cell donors
All potential haemopoietic stem cell donors must be typed for the HLA-A, HLA-B and HLA-DR.
If serological typing is used the minimum level of typing should be for the HLA Class I specificities listed in Table 15.2. Resolution to the level of broad antigen group, shown in brackets, is acceptable. If DNA-based typing is performed on donors a typing strategy should be employed that allows for HLA alleles to be defined to at least the two-digit level of resolution.
If HLA-DQ or HLA-Cw are tested they should be typed to the resolution shown in Table 15.2 if a serological method is used. For DNA typing resolution should be to the two-digit level. DNA typing for HLA-DQ can be limited to analysis of DQB1.
15.5.3 Investigation TAGvHD
Full HLA typing should be completed for the patient and all implicated donors. If serological typing is used the minimum level of typing should be for the HLA Class I and II specificities listed in Table 15.2. If DNA-based typing is performed on donors a typing strategy should be employed that allows for HLA alleles to be defined to at least the two-digit level of resolution.
15.5.4 Investigation of refractoriness
The investigation of refractoriness (see Figure 15.1) and the provision of selected platelets in such cases should comply with the BCSH Guidelines for the Use of Platelet Transfusions.(5) Serological investigation of suspected immune refractoriness requires screening for HLA Class I-specific antibodies only, but the screening technique must detect HLA-A, B, and C-specific antibodies. Any screen positive patient should be tested further for specificity to include all the Class I antigens listed in Table 15.3.
If a patient has HLA-specific antibodies that cannot be completely characterised or a specificity corresponding to any of the donor's HLA Class I antigens cannot be excluded then a crossmatch between donor and patient should be performed as described above.
15.5.5 Investigation of TRALI
Sera from all implicated donors must be screened for both HLA Class I and Class II-specific antibodies. Any screen positive serum should be further characterised for HLA class I and class II specificities to include all those listed in Table 15.3. See also Figure 15.2.
If any of the implicated donors are shown to have HLA-specific donors the patient should be typed for HLA Class I and Class II (Table 15.2) to determine the presence of alleles corresponding to the antibody specificities found in the donor(s).
If a donor serum has HLA-specific antibodies that cannot be completely characterised or a specificity corresponding to any of the patient's HLA antigens cannot be excluded then a crossmatch between donor and patient should be performed as described in Section 15.4.
15.5.6 Investigation of febrile transfusion reactions
If an investigation is requested, sera from patients should be screened for both HLA Class I- and Class II-specific antibodies. Any screen-positive serum should be further characterised for HLA Class I and Class II specificities to include all those listed in Table 15.3.
References
1. The European Federation for Immunogenetics (EFI) standards available at www.efiweb.org.
2. WHO Nomenclature Committee for Factors of the HLA System Report (see www.anthonynolan.org.uk).
3. Marsh, SGE et al (2004) Nomenclature for Factors of the HLA System, 2004. Tissue Antigens, 65, pp301–68.
4. Schreuder, G, M, Th et al (2004) The HLA dictionary 2004: a summary of HLA-A, -B, -C,
-DRB1/3/4/5 and -DQB1 alleles and their association with serologically defined HLA-A, -B, -C, -DR and -DQ antigens. Tissue Antigens, 65, pp1–55.
5. British Committee for Standards in Haematology (2003) Guidelines for the Use of Platelet Transfusions. British Journal of Haematology, 122, pp10–23.