Donating blood is read as giving a part of yourself for others. Dream books see it as generosity, or as a question of how much you can give before feeling empty.
When this appeared in your dream, what were you feeling?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.