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Compatibility testing prior to red cell transfusion is important to ensure blood group compatibility and detection of pre-existing atypical red cell antibodies.
Compatibility testing involves some or all of the following:
A request for a type and screen, also commonly referred to as a group and save, involves the following:
Determining the recipient's ABO and Rh(D) group
Performing a red cell antibody screen on the person
For patients who have a negative red cell antibody screen, a rapid serological crossmatch (such as the immediate spin crossmatch) or electronic crossmatch is performed to ensure ABO compatibility prior to the issue of the donor red cells.
Patients who have a positive red cell antibody screen require antibody identification and full serological crossmatching, using the indirect antoglobulin test (IAT). Specially selected donor red cell units should be made available prior to surgery.
Checking for previous or duplicate records, and then comparing current results with historical findings
If the patient has a history of having a clinically significant red cell antibody then a serological crossmatch (by IAT) may be necessary
When the patient has a clinically significant red cell antibody, red cells that do not have the corresponding antigen must be selected for crossmatching.
This is a final validation of compatibility between the recipient and the selected donor red cells. This may be performed by either serological or electronic means.
These techniques have been simplified in recent years, and only the 37 °C IAT crossmatch and immediate room temperature spin crossmatch remain in common use.
The IAT crossmatch is performed when the patient’s serum/plasma contains clinically significant red blood cell antibodies.
The room temperature immediate spin crossmatch has been retained primarily to detect ABO incompatibility.
An electronic crossmatch uses the hospital blood bank computer to perform a compatibility check on the compatibility between the recipient and the red cells selected for transfusion.
Electronic crossmatch and issue must only be used to confirm ABO and Rh(D) compatibility between the donor units and a current patient sample which has completed pretransfusion testing and has a negative antibody screen.
Sample validity refers to the period when a pretransfusion sample may be held for testing and used to provide crossmatched blood.
The sample validity period depends on the patient's transfusion and obstetric history.
Red cell antibodies can rapidly appear in response to stimulation by transfused red cells or as a result of pregnancy.
Consequently, if the patient has been transfused with red cells (or platelets), or is currently (or has been) pregnant in the 3 months preceding pretransfusion sample collection, the sample will have a validity of 72 hours. This is known as the 72-hour rule.
A new sample will need to be collected once 72 hours elapses if further transfusion is required.
Longer expiry times are often applied if the patient does not have have a history of transfusion or pregnancy.
We advise you to contact your transfusion service provider for their policy on sample retention.
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