You have to be registered as JW. That means they'll lose a lawsuit if they don't respect your wishes. I was raised JW, and I've had to fight about this because that's the only method people are sure works. You may get a doctor that doesn't believe you.

I donated to myself before I told the red cross I was dead so they'd leave me alone. I simply have a bad habit of answering questions precisely. I donated blood, and moved on. Then the day of surgery comes, and I express non blood alternatives as my preference. All the staff is confused. They come back with a bag of blood and say. " but this bag has your name on it. Is this your signature?"

The paperwork asked if I had any upcoming surgeries. I had donated so often it whooshed me!