To remove blood stains from sheets that have already been washed, use only cold water. Washing them in hot water can cause the blood to cook and set in the sheets. If they have already been washed, it is slightly more difficult to remove the stains, but not impossible.
To remove blood stains from sheets, use cold water, shampoo or mild dish soap, and table salt. Make the cleaning mixture with 2 tablespoons table salt and 1 tablespoon of dish soap or shampoo. Have the cold water nearby. Soak the stained area of the sheet in cold water, either in the bathtub or sink. Let it soak for about 15 minutes, then add the salt and shampoo mixture to the stain. Rub it in with a circular motion and rinse it with cold water.