CHICAGO — As a Jehovah’s Witness, Tracy Pickett always has enjoyed knocking on doors and introducing strangers to the tenets of her faith. But by the time she reached her mid-40s, scoliosis made every step excruciating and her spiritual mission impossible.Walking again would require surgery that often involves tremendous blood loss and a transfusion — a medical procedure to replenish the blood supply forbidden by her church. "Even though I love life and I don’t want to die, I want good medical care without blood," said Pickett, 49, of Crown Point, Ind.