Clinical background:
Pre-transfusion testing and routine antenatal screening. A valid group and save is required to determine the ABO and antibody status prior to the issue of blood products such as red blood cells, platelets and plasma. The ABO blood group has four principal types: A, B, AB, and O; there are two antigens and two antibodies that are mostly responsible for the ABO types. The specific combination of these four components determines an individual’s type in most cases.
ABO testing involves testing a person’s red cells for the presence or absence of A and/or B antigens (forward group) and also testing the same person’s plasma for the presence or absence of anti-A and anti-B antibodies (reverse group).
Antibody screen/detection is a test used to demonstrate the presence of clinically significant alloantibodies (capable of causing haemolytic transfusion reactions or haemolytic disease of the foetus/newborn).
This test is performed to predict compatibility between recipient antibodies and donor red blood cells. If the antibody screen is positive the next step would be to perform antibody identification. Transfusion or pregnancy may stimulate the production of unexpected antibodies against red cell antigens through either a primary or secondary immune response. The timing of samples selected for compatibility testing or antibody screening should take account of this, as it is not possible to predict when or whether such antibodies will appear.
It is also important to note that all cellular blood components contain residual red cells and may elicit an immune response. To ensure that the specimen used for compatibility testing is representative of a patient’s current immune status, the antibody screen should be performed using blood collected no more than 3 days in advance of the actual transfusion when the patient has been transfused, received a transplant or pregnant within the preceding 3 months, or when such information is uncertain or unavailable.
The 3 days includes the de-reservation period, e.g. if the sample was 1-day old, the blood would have to be transfused within 2 days. Where there has been no transfusion or pregnancy within the preceding 3 months, the sample is valid for up to 3 months.
Specimen container paediatric:
1mL K2 EDTA or 6mL K2 EDTA
Specimen container adult:
6mL K2 EDTA
Minimum volume paediatric:
1mL
Minimum volume adult:
6mL
Special requirements:
A group and antibody screen must be ordered via EPR PowerChart and taken with the BloodTrack bedside sample labelling system.
The Trust operates a zero tolerance policy. Deviation from Trust Sample Labelling Policy will result in the sample being rejected and a repeat requested.
Sample stability:
Short term storage: 24 hours at room temperature
Long term storage: 7 days at 4 to 6°C
Transport requirements:
Sample should be transported to Laboratory Medicine Reception via GP courier, hospital air-tube system or hand delivered to maintain storage conditions. Samples must not be subjected to extreme hot or cold conditions prior to testing.
Add on test:
Request for add on must be discussed directly with the Transfusion laboratory.
FH: 0191 2237849
RVI: 0191 2824435
Interpretation:
The presence or absence of antigens and antibodies is identified by agglutination. Agglutination occurs when the red cells are cross-linked by the binding of either IgG or IgM antibody molecules.
The pattern of reactions against a panel of reagents with known antigen or antibody status is used identify the antibodies or antigens present. The report will state the patient’s blood group and indicate whether alloantibodies are present or not.
Factors affecting result:
Wrong blood in tube or laboratory transcription error.
Addressograph stickers or e-Record labels on sample tube, samples received >24 hours from collection, incorrect specimen type received, clotted, haemolysed, icteric or lipaemic samples, insufficient plasma provided.
Clotted samples may interfere with instrument pipetting and must not be used.
Fibrin or particulate matter, clots, bubbles or scratches on the cassette can interfere with reaction interpretations.
Unexpected/discrepant results in the blood group must be investigated further and can indicate a previous transfusion, bone marrow or stem cell transplant, weak or variant expression of the D antigen, significant sub groups of A or B, presence of an alloantibody (usually cold reacting such as Anti-M), passenger lymphocyte syndrome in solid organ transplant recipients.