Removing blood stains from sheets that have already been washed can be done by soaking the sheet in cold water or cold diluted hydrogen peroxide. After that, it is recommended to use an enzymatic cleaner like Bio-Kleen or Zout Detergent in order to break down the enzyme bonds of blood molecules. Lastly, warm water and a mild detergent should be used to gently scrub away the stained area before rinsing out totally and air drying the sheet.