Here's a neat trick to get blood stains out of white sheets even after they've been set by the dryer. **EDIT** The following instruction is what worked for me, but please read through the comments before doing this. Some users found that using higher-strength peroxide resulted in tearing or fraying of the fabric after washing, and others have modified this instruction with different results. There is a lot of great feedback from those who shared their experience using this method, so please review the comment section before attempting. Thank you to all who have contributed.