Pre-Transfusion Compatibility Procedures (2012)


Key Points


-       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.


Quality Management


-       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


D Typing


-       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


Grouping Anomalies


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.


Antibody Screening


-       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 Identification


-       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



IAT Crossmatch

-       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:

o   Processes

§  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.


Link to guideline for more details + Practice IAT Panels