Understanding Blood Bank tests

If you need blood urgently, please telephone Blood Bank immediately!
For emergency transfusions, Blood Bank has various strategies to provide blood as rapidly and as safely as possible. See Emergency Blood
Group and screen results are only valid at the Blood Bank where the testing was conducted. If your patient has come from somewhere else with a different Blood bank, you will need to send a new sample to your Blood Bank.
Cord blood samples are not suitable for crossmatching due to the presence of Wharton's jelly.

All pretransfusion samples are tested for the ABO blood group and the Rh(D) blood group.
This is critical for preventing haemolytic transfusion reactions.
This is typically tested with the antibody screen so takes approximately 40 minutes but can be performed separately and faster in an emergency (but see Note below).
The results of these tests are compared with the patient's previous test results at this and other Blood Banks.
ABO is tested because all patients will have pre-formed ABO antibodies
Rh(D) is tested because it is highly immunogenic and the anti-D antibody is highly potent once formed.

An ABO/D card from an A positive patient

All pretransfusion samples are tested for antibodies to the other clinically significant blood groups.
There are 29 known blood group systems, each with more than one antigen.
For example, Rh is a blood group system, c, C, D, e and E are antigens within the Rh system.
This is critical for preventing haemolytic transfusion reactions.
This is performed by using the red cells from three different donors whose blood groups combined cover the full spectrum of clinically significant blood groups.
This takes approximately 40 minutes (but see Note below) and is typically tested simultaneously with the ABO/Rh(D) blood grouping. Because of the nature of the test, testing time cannot be shortened.
The test takes this long because there is a long incubation period to allow antibodies in the patient's plasma to attach to the donor red cells.
If the antibody screen is positive, antibody identification is needed.

A positive antibody screen

A positive antibody screen: clumps of agglutinated red cells in left two columns do not travel to bottom of of column

If the antibody screen is positive, an antibody panel of 11 different donors' red cells is used to identify which antibody is present.
This is critical for preventing haemolytic transfusion reactions.
This is typically a manual test and takes approximately 40 minutes if it is straightforward. But it can take longer - hours, days or even, in extreme cases, weeks.
Once the antibody has been identified, further time will be required to identify suitable units.
The test takes this long because there is a long incubation period to allow antibodies in the patient's plasma to attach to the donor red cells.

If the patient has been blood grouped twice (to exclude any errors) and has no antibodies on antibody screening, blood can be issued immediately by electronic crossmatch.
This is an electronic crossmatch because the Blood Bank computer system performs a number of crosschecks between the patient's results and the units for issue. If these checks are okay, the units can be issued as fully compatible.
For patients with no antibodies on antibody screening, blood does not have to be specifically put aside as all the ABO/D group-compatible blood in the bank is immediately available for issue.

An automated blood group analyser

Where a patient has antibodies identified on screening, a full crossmatch is needed.
A full crossmatch involves mixing the patient's plasma with red cells from the unit and looking for a reaction. It usually also requires confirming that the patient is negative for the antigen against which the antibody is directed. This may also take up to 40 minutes (but see Note)
The test takes 40 minutes (but see Note) because there is a long incubation period to allow antibodies in the patient's plasma to attach to the unit's red cells.
Multiple units can be crossmatched at a time, but Blood Bank will need to know how many are required to decide how many units to test.
Where a patient has antibodies identified on screening, only fully crossmatch units can be issued as fully compatible.
For some antibodies, a further step is also required, namely confirming that the unit red cells are negative for the antigen that the antibody is directed against.

Times provided above are the minimum time required to perform the test and do not include associated tasks.
The time to complete the test also varies depending on workload and case priorities.