Don't be tempted to toss a comforter in the washing machine with hot water when you notice a bloodstain. Since blood is a protein, hot water will "cook" it, causing the fabric fibers to coagulate, locking in the stain. Always use cold water when working on a bloodstain. Remove the stain as soon as you notice it; once it sets, the stain will be more difficult to remove.
Rinse the bloodstain under cold running water, rubbing the fabric together under the water.
Squeeze out the excess water and spray on some foaming shave cream, if the bloodstain does not rinse out. Work the shaving cream into the fabric like soap and rinse it out.
Soak the comforter in an enzyme presoak product if the stain remains. Follow the manufacturer's instructions on the ratio of water to enzyme product to use and the length of the soak.
Wash the comforter in the washing machine, using detergent and cold water. Don't put it in the dryer if any blood remains, as the heat will set the stain.
Apply three-percent hydrogen peroxide to a stubborn stain; add a drop of ammonia on top of the peroxide. Repeat the process until the bloodstain fades. Work in a well-ventilated area. Rinse the stained area well.