ABO grouping is the most important pre-transfusion serological test performed. Fully automated ABO and D grouping procedures have significantly improved the accuracy and security of results, and should be used wherever possible.
When anomalous ABO groups are encountered laboratory protocols should support investigation of the following findings.
Missing agglutinins in reverse grouping:
Unexpected additional reactions in the reverse group:
Unexpected reactions in the forward or D grouping, including positive diluent control:
Unexpectedly weak or mixed field reactions in forward or D group:
Genotyping is useful in resolving grouping problems, particularly weak and partial D types (see section 15.2). Genotyping alone must not be used to determine the ABO group for use in selection of blood for transfusion. Where the patient ABO group cannot confidently be assigned by serology, group O (high-titre negative) blood must be selected.
In all cases of the investigation of alloantibodies laboratories should focus on:
When antibodies which cannot be identified have been detected, laboratories should consider referral to the International Blood Group Reference Laboratory (IBGRL).
When patients with rare phenotypes are encountered, laboratories should, when practicable, exchange material with other RCI departments via the UK Rare Red Cell Exchange to ensure continued supply of valuable materials.
Antibody identification techniques and protocols are described in BCSH guidelines and should be adhered to. More complex problems encountered by RCI laboratories and not covered by BCSH are considered below.
When investigating complex antibody mixtures RCI laboratories should consider:
Antibodies traditionally known as HTLA include anti-Ch, –Rg, –Kna, McCa, –Yka, –Csa and –Sla. Typically HTLA antibodies present as reacting with most panel cells by indirect autoglobulin test (IAT) with variable strength, with or without similar patterns using enzyme-treated cells. Experienced operators can recognise characteristic agglutination by microscopic examination of tube IAT, which have been described as ‘loose’, ‘stringy’ or ‘gritty’. In investigating samples suspected to contain HTLA antibodies RCI laboratories should consider:
Typically antibodies to HFA present with positive reactions of similar strength against all routine screen and identification panel cells. The most commonly encountered specificities include anti-k, –Lub, –Kpb, –Vel, –Coa, –Yta, –Fy3, –U and –Inb. In investigating samples suspected to contain antibodies to HFA, RCI laboratories should consider:
Typically antibodies to LFA present with negative antibody screen and are detected in crossmatch. The most commonly encountered specificities include anti-Kpa, –Wra and –Cob. In investigating samples suspected to contain antibodies to LFA, RCI laboratories should consider:
Autoantibodies are frequently encountered in pre-transfusion testing, and may be the cause of autoimmune red cell destruction, or may be clinically benign. In either case autoantibodies may interfere with pre-transfusion testing, either due to coating of patient’s cells with immunoglobulin, or as pan-reactive antibody in patient’s plasma. In providing safe transfusion in the presence of autoantibodies, RCI laboratories may adopt the following strategies.
Most modern test systems support routine, accurate grouping of the majority of patients whose cells are coated with immunoglobulin and who give a positive DAT. Cases which are problematic may present with reaction patterns that cannot be assigned to an ABO group, weak additional reactions and positive reagent controls. Such cases should be investigated as in section 13.3.1.
Laboratories should make a clear documented assessment, based on the recommendations of reagent and test system suppliers, how to manage cases with anomalous ABO and D groups. This is particularly important when potentiated reagents are included in test systems.
In dealing with cross-reacting autoantibodies, which complicate the detection and identification of underlying alloantibodies, RCI laboratories should consider:
Consideration should be given to close matching of recipient and donor red cell types. This is to safeguard against the presence of alloantibodies undetected by tests on modified plasma, and to prevent further alloimmunisation. In patients who cannot be grouped by conventional serology, due to sensitisation of red cells or previous transfusion, genotyping offers a solution.
In patients with autoantibodies requiring regular transfusion, close matching of transfused red cells with the patient’s own phenotype, to manage risk of transfusion reactions, may be used as a basis by scientists and clinicians to assess, and potentially reduce, the required frequency of testing. Such assessments should be fully documented and subject to planned review.