Everyone, ex-JWs, JWs, and never been JWs should have a healthcare proxy.
I agree with Blondie. There's so much more than just blood at stake.
Also, consider my experience last summer. If you've ever been treated at your local hospital, you may find yourself in an unpleasant situation at a real bad time.
http://www.jehovahs-witness.com/16/95897/1.ashx
-Denise.