Although the doctors all insist it is not possible, my daughter's blood type changed from A+ to O+ during her lifetime. She was typed at birth as A and told when she joined the military she was O. I thought it was a mistake, but then she had a child and was tested again and told it was O. Another interesting thing with her, the color of her eyes changed from a dark brown to a very pretty green when she was around 17 years of age. The doctors also said this is not possible.