Here is the short lesson on blood stain removal: act quickly.
Most carpets today come with stain-resistant treatments, so even
blood can be removed if you get it right away. The longer you
delay, the more difficult removing any stain becomes, and there
are no stain-proof carpets (yet). With blood, the process of
coagulation makes it especially hard to clean the spot once it
has been around a while.
Removing Blood Stains Step-by-Step
1. Rinse and extract the blood with cold water. Use just a
little at a time, so you don't spread the stain. Hot water will
set the stain, possibly making it permanent, so use only cold
water. Just add water, then blot it up with a clean white cloth
or white paper towels. Alternately, you can suck the solution
out with a shop-vac, which means less of a chance of spreading
2. Try to remove the remaining stain with a solution of a
few drops of Dawn dish washing detergent in a cup of cold water.
Work it into the blood stain, but be careful not to spread the
stain or rub so hard that you damage the carpet fibers. Damaged
fibers hold stains.
3. Repeat as many times as is necessary, or until there is
no more transfer of the stain from the carpet to the cloth or
paper towels. Blot up excess water when you are done.
Instructions continue after this
video, which shows you how to remove blood stains using liquid
dish washing detergent and amonia (and water for rinsing, as
always). It also provide two alternative methods. Scary looking
4. If you have a fan, leave the fan blowing on the area to
dry it quickly. Otherwise set a stack of paper towels (white)
on the stained area, or a couple clean white cotton cloths, and
put something heavy on them. Leave this to blot up the remaining
liquid, replacing the cloth or paper towels if necessary. Fast
drying assures you that any remaining stain deeper in the carpet
doesn't "wick up" to the surface and become visible
Some people have reported that club soda can help remove blood
stains, so if the above instructions don't work, you can try
that. It's not always easy to predict which stains will come
out and which are permanent until you try removing them. This
is due to the various types of carpet fibers and other factors.
Natural fibers are usually more difficult to remove stains from,
Hydrogen peroxide might get blood out of the fibers also.
Use the 3% (the common variety) formulations, and apply it a
few drops at a time. Dab at the spot with a clean white cotton
cloth to see if you are getting transfer of the stain to the
cloth. As long as you are, keep repeating this process. When
you are done, dry the area quickly.