Thanks for this, I noticed a few donations ago that I got a blue tag and wondered what it was forI always thought that too and you're absolutely right in the vast majority of cases.
O neg is split into 2 groups
O neg neo
O neg neo is a purer form of blood donation that has no viruses like Cytomegalovirus (CMV)
There is a small group of people who, because of a reduced immune system (eg newly born babies) need the Neo version as their body can't fight CMV so need the Neo neg.
If your donation is O neg neo, your bag gets a blue label attached
View attachment 48598
For those interested, there's more info here...