DayZ field wiki · Medical
Blood test kit
Read the card before the tube
Short answer
A bag of the wrong blood is not a heal. The kit exists so you stop guessing.
Also: blood test · type kit
How it works
Types exist. The test kit writes the letter so the bag matches. Saline is the safer fill when you don't know.
What to do
Test before you take. If you don't have a kit, saline.
Don't
Don't both donate at once unless you want two slow people.