Pre-Transfusion Compatibility Procedures (2012)
- The process of determining eligibility for Electronic Issue must be controlled by the LIMS and not involve manual intervention or decision-making.
- If DAT is positive for patient transfused within the last month then an eluate should be prepared to test for presence of specific alloantibodies.
- Blood Safety and Quality Regulations (BSQR) introduced in 2005 by the EC
- Key domains
o Quality Management Systems
o Staff Training and Competency
o Reagents and Test systems
o Information Systems (LIMS)
o Automated Blood Grouping and Antibody Screening Systems
- G&S must be taken no more than 3 days before actual transfusion if patients have been transfused or pregnant within the previous 3 months (or if there is uncertainty).
- In chronically transfused patients with no alloantibodies, or pregnant women with no alloantibodies, samples can be considered suitable for up to 7 days but this must be documented on a patient-by-patient basis.
- In all other cases, samples are valid for 3 months.
- A pre-transfusion sample must be stored for a minimum of 3 days post-transfusion in case of acute haemolytic transfusion reaction.
- Once a patient is known to have formed a red cell alloantibody, every new sample needs full testing to exclude any new antibodies.
- A second sample for confirmation is required for a first time patient prior to transfusion.
Situations where is might be appropriate to omit the Reverse Group
- Neonates – as any ABO antibodies are likely to be maternal
- In patients who have previously had a full grouping and where, for the new sample, secure and fully interfaced automation has been used. Risk assessment must consider possibility of wrong blood in tube (1 in 2000 samples)
- Pos and Neg controls should be used regularly, as a minimum:
o Every 12 hours that an analyser is in use
o When changing lot numbers
o When starting up a new analyser
- When automation used, D typing can be performed using a single IgM monoclonal anti-D reagent, which should not detect DVI.
- DVI most significant D variant. Will show as D+ with some reagents, but patient is capable of being stimulated to produce Anti-D. Due to risk of HDFN, these patients need to be considered as D- if female and of child bearing age. Hence, best to use a reagent that will not detect DVI and so type the patient as D-.
- The term ‘D Variant’ now encompasses both weak and partial D
- Partial and Weak D, historically:
o Weak D thought not capable of making anti-D and so could be considered D+
o Partial D can make anti-D to the epitopes it lacks and so considered D-
- However, increasing evidence suggest both capable of making anti-D, so use flow chart
D Typing Flow Chart Summary:
Is the reaction grade with one or more anti-D reagents positive but weak ('weak' is locally defined)?
- If no, report and treat as D positive
If yes, Is the patient female and <50 years old and/or are they likely to require chronic transfusion support?
- If no, report and treat as D positive
- If yes, treat patient as D negative and refer for confirmation of D type
Causes of a Mixed field reaction
- ABO D incompatible / mismatched transfusion
- Mismatched HSCT
- A3 or B3
- Large FMH
- Twin to Twin Transfusion
Intrauterine Transfusion – neonates may appear to have same ABO D group as the transfused cells for several months post-delivery due to bone marrow suppression.
Cold-active alloantibodies – unexpected reverse grouping result may be obtained if these cells express an antigen for which a cold-active alloantibody is present in the patient’s plasma other than anti-A or anti-B. Where possible repeat at higher temperature.
A/B Variants – Variant A and B may give weak or negative reactions with monoclonal reagents. Refer samples to a reference lab.
Other reverse group anomalies – Potentiators in the reverse grouping reagents may cause IgG antibodies (e.g. anti-c) to be detected in the reverse group.
- Low Ionic Strength Solution (LISS) IAT is considered the most suitable for detection of clinically significant antibodies, due to speed, sensitivity and specificity.
- Minimum specification for screening set:
o One red cell should be R2R2, and the other R1R1 (or R1wR1)
o K, k, Fya, Fyb, Jka, Jkb, S, s, M, N, P1, Lea, Leb
o At least one cell should be homozygous for Fya, Fyb, Jka, Jkb, S, s
- Antibody specificity should only be assigned when the plasma is reactive with at least two examples of reagent red cells expressing the antigen and non-reactive with at least two examples of reagent red cells lacking the antigen.
- Important to recognize limitations of the panel in use. A single panel might not always detect common combinations of antibodies and labs should be aware of their specific panels deficiencies.
- In cases where all panel cells are positive but the DAT or Auto are repeatedly negative, a high frequency antibody should be suspected à Reference lab. E.g. anti-HI is found in non-group O patients and its presence needs to be excluded using an IAT panel composed of ABO cells of the patients’ type.
- Red cells Treated with Papain Enzyme will give:
o Negative reactions for Rh, Kidd, P1 and Lewis antibodies
o Enhanced reactions for MNS and Duffy antibodies
o Unchanged reactions for Kell and Lutheran antibodies
Selection and Issue of Red Cells
- Detects ABO and non-ABO red cell antibody incompatibility
- Default technique for when electronic issue is contraindicated
- IAT crossmatch must be used when:
o Patient’s plasma is known to contain red cell alloantibodies of clinical significance
o If the antibody screen is positive
o For neonates and fetuses as maternal IgG is present
o Following incompatible HSCT
o Following incompatible solid organ transplant within last 3 months (IgG anti-A or atni-B produced by passenger lymphocytes)
- Requires a positive control with every cross match.
Electronic Issue (EI)
- The selection and issue of red cell units where compatibility is determined by the LIMS without serological testing of donor cells against patient plasma.
- Safe use of EI depends on:
o Adequate Quality Management Systems and laboratory processes
o LIMS controls the issue of the blood product
o The specific patient’s transfusion and antibody history + serological status of the current sample
- EI is permissible if all of the following are met:
§ Testing and result entry of the G&S are fully automated
§ Reagents, cells and technology meet BCSH criteria
§ Unique bar codes are used for sample and reagent ID
§ Results are transmitted electronically from analyser to LIMS
§ LIMS controls the suitability of patients and their samples for EI
§ LIMS enables permanent exclusion of patients from EI where appropriate
§ LIMS enables temporary exclusion of patients from EI
o Patient Sample
§ Blood group ID is identical to historical record
§ No manual amendments have been made
§ Current antibody screen is negative
§ G&S result are complete and fully authorized by LIMS
§ No previously known antibodies of clinical significance
§ Patient not excluded on clinical grounds
§ Meets sample storage time requirements.