At least last time I donated blood in my country (Canada), you could discretely indicate "do not use" by applying a different sticker to the bag. This was done in case someone got peer pressured into donating but didn't want to reveal something private that would have disqualified them otherwise.

[–] saigot@lemmy.ca 10 points 5 months ago

Yes but they also test the blood and will call you if they have reason to believe you are positive.

[–] emergencyfood@sh.itjust.works 10 points 5 months ago

We (India) don't have that, mainly because blood bags don't grow on trees, but there's a question about sleeping eight hours the previous night that always seemed irrelevant. Now that I think about it, it might have been added for this purpose.

[–] FreshLight@sh.itjust.works 5 points 5 months ago

Roughly the same here in Germany