Antibody Investigation
Clinical Background
The BT laboratory will request an antibody investigation when a positive reaction is detected in the antibody screen. Blood group antibodies of the ABO system are universally common, but those of other blood group systems are only produced when red cells are transferred to a patient via a blood transfusion or a fetal red cell bleed during pregnancy. Theoretically, any antigen present on the transferred red cells which are not also present on the patient’s own red cells may be recognised as foreign by the recipient’s immune system and produce atypical antibodies.
However, this does not routinely occur, and antibody stimulation is dependent on a number of factors including the immunogenicity of the antigen involved. Rarely, these occur naturally without a stimulus and are sometimes auto-antibodies i.e., directed against the patient’s own red cells. When an atypical antibody is detected (antibody screen) it must be identified to allow for provision of compatible blood. This is especially true of antibodies that are clinically significant. These antibodies are capable of causing either transfusion reaction and/or haemolytic disease of the fetus or newborn (HDFN). Where it is not possible to identify the antibody (or antibodies) present the samples may require referral to an NHSBT reference laboratory. Blood group antibodies are only important to the patient when they require a blood transfusion or are pregnant.
| Sample Stability | Short term storage: 24 hours at room temperature. Long term storage: 7 days at 4-6°C |
|---|---|
| Transport requirements | Sample should be transported to Laboratory Reception via 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. |
| 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 on sample tube, samples recieved >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. |
