Discussion
Testing of EQA samples should, as far as possible, replicate testing for patients. Only one EQA sample should be taken out and tested at a time, and the same level of good clinical practice should apply as with clinical samples.
If a patient who is a CYP2C19 poor or intermediate metaboliser is incorrectly genotyped as normal metaboliser, they may be prescribed clopidogrel without dose adjustment or an alternative antiplatelet therapy. This could result in reduced drug efficacy and increased risk of adverse cardiovascular events due to insufficient platelet inhibition.
Conversely, if a patient who is a normal metaboliser is incorrectly genotyped as a poor or intermediate metaboliser, they may be prescribed an alternative antiplatelet therapy unnecessarily. While these alternatives are effective, they may not be the first-line treatment, and their use may increase the risk of side effects or cost.
If a patient receives a test fail, they may experience delays in receiving appropriate antiplatelet therapy. Repeated test failures should be investigated to identify potential issues with staff training, workflow, or equipment.
Sample Concordance and Scoring:
EMQN aim to provide swabs with a range of cell loads. Scoring for test failures has been graded, so that the penalty is lower for swabs at lower cell loads.
Concordance of results between centres participating in the survey is monitored by EMQN. Scoring will be adjusted based on concordance. Samples that have had scoring adjusted due to concordance will be marked with an asterisk (*). A summary of the scoring and performance calculation can be found in the appendix of this document.
