A Johnston woman has become only the third person in the United States to donate a kidney to a stranger. Dr. Cass Franklin performed the operation, taking 30-year old Shelli Brennan’s kidney and transplanting it into 27-year old Ann Prather of Des Moines. Franklin says donations normally come from someone who has died, and he first thought the whole thing was a prank. But he says Brennan passed all the normal tests for a donor — including a psychological evaluation. He says Brennan is an extraordinary person who “has a calling from a higher level” who wanted to help someone.Cass says Brennan had discussed the decision to donate her kidney with her husband and family for a year before going ahead with the surgery. In another unusual twist, Prather and Brennan met the day before Wednesday’s surgery.He says Prather is doing well after the transplant and Brennan should go on to live a normal life.The average wait for a donor kidney is three years and Cass has no problem with using live “Good Samaritan” donors.While there have only been three such donations, Cass expects there to be more across the country.Cass says both Brennan and Prather want to maintain their privacy and asked that he be the only person to talk to the media about the donation and transplant.