Dried blood is a challenge to remove from many fibres but especially from carpets and upholstery. It's not possible to flush the blood through the fibre with lots of water. Once the blood has dried, it binds with the fibres in the carpet, according to the How to Clean Anything website. Fresh stains are easier to remove than old dried stains. As soon as you become aware of the stain, take steps to clean the carpet.
Brush as much of the dried blood off of the carpet with a stiff brush.
Vacuum the dried blood up.
Combine 1 tbsp of dish washing liquid -- not dishwasher liquid -- with 2 cups of cold water.
Soak a clean white cloth in the mixture. Wet the blood stain by pressing the cloth against the stain.
Blot up as much of the liquid as possible with a dry towel.
Repeat soaking and blotting until the stain is removed. If the cloth is no longer absorbing any of the stain, treat with an ammonia mixture.
Combine 1 tbsp of ammonia with 1/2 cup of water. Blot the stain until is saturated.
Cover the stain with a 1-inch thick layer of paper towels. Weigh the towels down with a heavy book. Remove after 30 minutes. The towels will absorb the remaining stain.
Let the carpet dry for 24 hours. If a brown stain comes back, saturate with a mixture of 1 part white vinegar to 2 parts water. Blot the stain. Cover with a thick layer of paper towels and heavy books. Remove after 30 minutes and let air dry.
Avoid breathing ammonia fumes. Do not scrub the stain; that only drives it deeper into the fibres and spreads the stain.
Use the vinegar and water treatment only once per stain.