Fresh blood stains on bedding, such as a comforter, are relatively painless stains to remove. Dried stains can also usually be removed, as long as the comforter has not yet been laundered. Once a blood stain has been laundered and dried, it is nearly impossible to remove, as heat sets the stain. You can, however, use the same stain removal techniques on fresh or dried blood to fade a set-in stain. The key to completely removing fresh and dried blood stains is to treat the stains as soon as possible.
Drench the area in cold water if the stain is still fresh and wet. Rub the sides of the fabric around the stain together. If the stain has dried, wet the area thoroughly with water.
Drop a small amount of hydrogen peroxide onto the stain directly (if the fabric is light colored). If the fabric is dark, omit the peroxide; instead, rub the bar of soap onto the stain, getting the lather deep into the fibers.
Place the comforter into the washing machine and add laundry detergent and color safe bleach according to the manufacturer's instructions.
Launder the comforter on a "cold" setting.
Pull the comforter out and examine the stain. If any residual blood stain remains, repeat the steps. Do not dry the comforter until the stain is removed because heat will set the stain into the fabric.