Marloes, Theo and Eva conducted a large scale register study in the Netherlands to answer this question. Here are some main takeaways:
Temporary deferral often deters donors from returning to the donation center for a subsequent donation.
Deferral reason and donor experience individually as well as jointly impact donor return.
Particularly first-time and reactivated donors are at risk of dropping out, especially when deferred for haemoglobin or short-term medical reasons, respectively
💡 Check out the full paper HERE for more interesting details if you are a blood bank employee and if you are a researcher, for some ideas for future research check the Discussion section.