One of the cleanings I was at today was indeed, blood. Unfortunately, the client cut open her foot on a piece of glass and bled quite badly all around her home.
The thing with blood is (and this applies to most spills) to try and blot up what you can, never scrub, that just spreads it out. A teaspoon of dish soap in a spray bottle is a good thing to have. Spray on the area and blot some more. If you can get it all, thats great, if not, call for an appointment to remove the residue. If you do get it all out, go over the area with a little clear vinegar, this will help to neutralise the soap and prevent the area from picking up soil, getting really dark and ultimately, difficult to clean.
On this occasion the blood had dried and more extreme measures were needed. A pretreatment with an enzyme based product and even rust remover (yes really). Used one after the other this worked and now the rooms are clean again.
Stephen, the Carpet Cleaner