Pre-Transfusion Compatibility Procedures (bsh 2012)


Key Points


The process of determining eligibility for Electronic Issue must be controlled by the Laboratory Information Management System (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

  • Quality Management Systems

  • Staff Training and Competency

  • Reagents and Test systems

  • Information Systems (LIMS)

  • 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:

  • Every 12 hours that an analyser is in use

  • When changing lot numbers

  • 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:

  • Weak D thought not capable of making anti-D and so could be considered D+

  • 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

  1. ABO D incompatible / mismatched transfusion

  2. Mismatched HSCT

  3. A3 or B3

  4. Large FMH

  5. 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:

  • One red cell should be R2R2, and the other R1R1 (or R1wR1)

  • K, k, Fya, Fyb, Jka, Jkb, S, s, M, N, P1, Lea, Leb

  • 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 —> 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:

  • Negative reactions for Rh, Kidd, P1 and Lewis antibodies

  • Enhanced reactions for MNS and Duffy antibodies

  • 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:

  • Patient’s plasma is known to contain red cell alloantibodies of clinical significance

  • If the antibody screen is positive

  • For neonates and fetuses as maternal IgG is present

  • Following incompatible HSCT

  • 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:

  • Adequate Quality Management Systems and laboratory processes

  • LIMS controls the issue of the blood product

  • 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

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