Hi, Malcolm has alerted me to the query regarding the UK NEQAS samples. Whilst the last thing we intend to do at UK NEQAS is to trick and confuse our participants, I acknowledge that there are some issues with distributing diluted antibodies for identification. The premise of EQA requires that all participants test the same material, and this means we have to produce a 2 to 3 litre pool for each EQA sample. Therefore, we have no choice but to use diluted antibodies, and in some cases the enzyme activity can be lost at a lower dilution than the IAT activity. This is a limitation of the UK NEQAS exercises, but the alternative is to only be able to use a severely limited range of specificities. I agree that you would expect Kidd antibodies to react in a reliable 2-stage enzyme technique. However, I would not be prepared to exclude Kidd antibodies due to lack of a reaction in an enzyme technique, and especially not where the reactions by IAT indicate that they might be present. The EQA samples are tested by all IAT technologies in common use in the UK (Tube, DiaMed, BioVue and Capture), and are not scored if not identifiable by IAT at the closing date of the exercise. We are careful not to distribute Kidd antibodies that don’t react well in enzyme in combination with an antibody non-reactive by enzyme e.g. Fya, as this is the situation where the lack of reactivity of the Kidd antibody by enzyme is most likely to increase the degree of difficulty of identification. As part of the educational aspect of the exercises we advise the use of an ‘enzyme IAT’ to confirm the presence of a weak Kidd antibody (that maybe reacting only with apparent homozygous cells), or to make an exclusion in the presence of other specificities. Enzyme IAT should enhance the reactions with antigen positive cells in real and EQA samples. So Malcolm is right - it is probably more to do with this particular EQA sample than with the enzyme technique.
