Fresh blood is often easiest to remove, but even dried blood can be removed with cold water and dishwashing detergent. Ammonia works as a stain removal option if the detergent alone isn't enough to remove the dark red stain.
Preparing Dried Blood Stains
If the bloodstain has already dried, remove some of the hardened blood by brushing the carpet with a steel brush. Be careful not to snag the carpet with the brush. Vacuum up the dried blood if you loosened a significant amount.
Removing With Dish Detergent
Start with dish detergent -- it's a gentle way to remove the blood, whether dried or fresh. Always use cold water when removing bloodstains from carpet. Removing bloodstains takes lots of elbow grease and patience. The blood won't likely come out completely on the first try.
Combine the dish detergent and cold water in a clean container.
Dip the clean cloth into the soapy water mixture. Dab the cloth gently on the bloodstain. Continue blotting the stain with the soapy cloth until the blood releases from the fibers.
Rinse the cloth as needed between dabbing. Keep several clean cloths handy. Switch to a clean cloth after the first cloth becomes stained with blood. If you use the same rag, the blood will get back on the carpet and make the stain worse.
Dab the spot with clean water and a clean cloth after the bloodstain is gone. Use a dry cloth to blot the carpet to dry it.
Removing With Ammonia
Ammonia is an option for cleaning a stubborn bloodstain. Combine 1 tablespoon ammonia with 1/2 cup of water. Use the same dabbing method with a clean cloth as you used with the dish detergent. Follow up with a cold water rinse with a clean cloth after the stain removal.
Hydrogen peroxide is another household item that may help with blood removal. Test the peroxide on a hidden area to ensure it doesn't discolor the carpet. Dab the hydrogen peroxide into the carpet as you did with the water and detergent.
Using Stain Removers
Commercial carpet cleaners and stain removers offer another option. Enzymatic-based cleaners may work on bloodstains, because blood is a protein. Apply the cleaner or stain remover to saturate the stain. Allow it to stay on the carpet for up to a few minutes before dabbing with a clean cloth to remove the cleaner and blood. Dab the area with fresh water and a clean cloth to remove the cleaner from the carpet.