Um, I don't really know where you live but if you have a Giant nearby, they have this stuff, it comes in a weird shaped yellow bottle for blood stains. It works really good, so I'd get that. Hope this helped! :)
A product call "Awesome", yellow color liquid, will probably do it without discoloring or bleaching white, your carpet. It's available at Dollar General, Family Dollar, Dollar Tree, and others. Good luck.
I have so many questions of wondering what the hell happened in the first place to there even being blood on the carpet which is probably soaked through by now like maybe if something due to you committing murder then you might want to check yourself in to the local authorities. And about that blood stain you could use Hydrogen Peroxide it would bubble up all the blood and clean the carpet not taking the color out of it at the same time. Anyways how come you even didn't tell us all exactly in details what that blood stain was from?