Because of the difficulty of storing blood, the ship does not keep a blood bank. Instead the crew sign up to be called upon to give blood when needed. I registered with the nurse back in January and yesterday I got a call from the lab to come down and have a couple of vials taken so that they can test my blood to check I am a viable donor. It will take 3 weeks or so to process the tests and then I will be added to the list of donors.
We are currently very short of B and AB donors so Sarah (who is O-neg and therefore a universal donor) will likely be in top demand! My O-pos is slightly less useful although I hope to get the chance to do my bit.