[Delayed adverse reactions to blood donation: From haemovigilance data to specific studies]

Delayed adverse reactions to blood donation occur after the donor left donation site. Their intrinsic gravity and possible complications can be increased by the fact the donor is alone. This can also increase bad memories, leading to a donation giving up. Blood transfusion centre is only aware in case of donor feedback, hence an event underrating. We choose to compare our data upon delayed adverse donor reactions with those we could find in past studies.A first data level comes from French haemovigilance data while serious adverse reactions declaration is mandatory. But a second level can be reached using blood transfusion centre computerized data because all the donation reactions are saved whatever the gravity is. In both cases, delayed reactions are only those reported by donors. We try to make an exhaustive search of specific studies upon the real delayed reactions incidence so as to compare with our data.There were 1957 serious adverse reactions declared in our regional haemovigilance database between 2011 and 2015: 49 % occurring during donation, 40 % after it but before donor departure, and 11 % delayed events. There were 16,050 adverse reactions recorded during the first trimester of 2016 in mainland France, with 2.7 % delayed ones. Proportion of delayed events rises when gravity rises, until 27.6 % for the most serious ones. It varies between 2.2 % and 2.7 % for vasovagal reactions, haematomas, and other local reactions, and reaches 16.2 % for other general reactions. Data found in other studies with a spontaneous donor notification are of the same kind. But four studies soliciting specifically donor notification give a dramatically higher delayed reactions incidence, with an understatement greater than three out of four. Moreover, these studies found a majority of delayed reactions, which are not included in haemovigilance like fatigue or bruising.Occurrence of a delayed donor reaction is clearly underrated in standard haemovigilance. It remains to be seen whether it have the same impact on donor return as immediate reactions. Considering that delayed reactions are much larger, it might be interesting to take them into account in the evaluation of strategies dedicated to lower immediate reactions.