QC checks for ABO typing reagents; what is required for compliance with rules/regulations versus what is needed to assure test results are accurate for patients who might need transfusion?
A Clinical Support Officer at a blood service in New Zealand is seeking views on daily QC checks required for ABO typing sera for both tube testing and column agglutination testing (CAT) methods (manual and automated) as used for pretransfusion testing of patients. He reports that in New Zealand they follow the Australian and New Zealand Society Of Blood Transfusion (ANZSBT) 'Guidelines For Pretransfusion Testing' (2002) and amendment which require (1) that the manufacturer's instructions are followed and (2) that according to section C 1.1 ABO Grouping Reagents: "A system shall be in place to confirm the specificity of ABO grouping reagents. ABO grouping reagents shall be confirmed against A2 and B cells. A1 and B cells are required for reverse grouping". He feels that there is a slight contradiction in the above requirements, as the reagent manufacturers often recommend the use of A2B cells. Furthermore, he feels that traditional QC of ABO sera would use A1 and B reverse grouping cells and a group O cell. If the use of A2 cells is truly required, that would mean they would have to separately purchase A2 reagent cells in addition to routine reverse grouping cells (A1 and B), often as part of a relatively expensive 'QC' kit. The particular point they are currently debating within their organization is whether or not it is even necessary to use group A2 red cells to confirm the specificity of anti-A reagents. It is argued on one hand that because of the nature of modern monoclonal reagents in respect of potency, avidity, specificity, stability etc., that there is nothing to be gained from testing the anti-A reagent with a weak expression of the A antigen, as such testing will not normally show any observable difference in reactivity compared with testing A1 red cells. The contrary view is that QC using weak expression of the target antigen provides reassurance that (1) the reagent routinely detects weak form of the target and (2) using cells with a weak expression allows earlier detection of problems with the antisera e.g. incorrect reactivity, loss of potency etc
In response to the above question, W. John Judd, FIBMS, MIBiol, Professor of Immunohematology at the University of Michigan (attribution used with permission) comments that given that much of QC is done to satisfy those who regulate us, with regards to the QC of ABO testing it matters not if you use A1 or A2 cells. However, speaking hypothetically, if one wants to document that each technologist performed their tests correctly and the reagents worked at each time of use, and had not deteriorated significantly, you would want to use RBCs with the weakest antigen expression. Thus, for the aforementioned hypothetical situation, it would be preferable to use A2 red cells for the QC exercise. However, in actual practice and in his opinion, no daily QC of ABO typing reagents is necessary when testing patients. Rather, it should suffice to document on a daily basis that "All conflicts between RBCs and serum ABO typing results were resolved, and test results from current samples were in accord with previous results, when available." He concludes by asking "Has anyone encountered a QC problem with ABO typing reagents?"
The following responses have been received.
ADDENDA Oct. 4, 2005
- A Transfusion Service Supervisor in Florida reports that in recent years her laboratory experienced a QC failure of a single vial of a monoclonal anti-A typing reagent. The vial in question was delivered to her laboratory as part of a "ten-pack" and was the first vial of that package to be opened. Upon performing QC on the vial, the antisera did NOT react with A1 or A2 cells of either patient or reagent manufacturer origin. (Note: they tested the A2 cells only as an investigative procedure; their routine QC uses A1 cells.) However, upon performing QC on the other nine vials, the reagents within reacted as expected. She reports that they contacted the reagent manufacturer and returned the faulty vial to them. After testing the faulty vial, the reagent manufacturer reportedly agreed that the reagent did not react with A cells, and hypothesized that the problem must have been with "reagent storage conditions during shipping or by the facility ". The Floridian responded that the faulty vial had been stored by their laboratory in the original package and in the exact same manner as the other nine vials until the QC testing was performed, yet all nine other vials reacted as expected. She adds that although the faulty vial was found by "QC testing", she agrees with Professor Judd that this problem would probably have been found when the serum and cell grouping tests did not agree or current results did not agree with previous results. However, this case represents an example which should reinforce to staff why QC is done, and why such QC is vital when there is not a "second check" of a serum (reverse) type, or previous records to compare against current results, etc. She concludes that the lesson learned is as follows: The vial does not always contain what the label says!
ADDENDA Nov. 21, 2007
- A colleague reports that
a network of five hospitals in Florida performs pre-transfusion ABO testing via different methods
including tube, gel-based and automated gel-based. One of the hospitals
is using both positive and negative controls for
QC of ABO grouping antisera for the tube method (i.e. anti-A is tested against an O cell for a negative
control), whereas the rest of the hospitals in the system are using positive
controls only, since patient testing results provide a double check of
reagent performance. They would like to standardize practices throughout
the system and would like to know how other institutions currently accomplish
QC for ABO grouping reagents.
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