I would think so, if it was enough. I do animal rescue and I wash a lot of stuff with unpleasant things on them. I realize urine has a different make up than blood. However, when I wash something a sick animal has pottied on, particularly with these newer washing machines, I feel like there's residue left in the drum and it needs to be put through a self clean cycle afterward.
In all likelihood they have a newer machine. I have done a lot of research on both the front loaders and top loaders that are sold now (and I can tell you that top loaders with the old agitators are difficult to get and have very limited models available). Here's what I know from research and experience on both types:
Front loaders often hold actual dirt, hair, lint, and other residue under the rubber lip of the door and it is VERY difficult to clean thoroughly. (For this reason, and the minimal amount of water used, allergists recommend not buying one and getting rid of them if you have one and have autoimmune issues or allergies.)
The new top loaders without the center agitators also use less water. In fact, if you do a YouTube search you will find all kinds of videos about clothes not getting clean or fully rinsed. There are ways around this because you can no longer manually set a load size in most. It goes by the weight of the clothes. So to get things fully cleaned and rinsed, many people are tossing in a bucket of water first to make the clothes heavier and trick the machine into using more water.
OK, so last thing about some of these top loaders is that even when you add more water, wash on heavy cycle with an extra rinse, your machine may still smell potent after washing something stinky, which leads me to believe that there IS residue left behind in the drum, or even perhaps between the drum and the outer case.
Blood does not smell so he would not notice such but if he's smart he would follow up with a self clean cycle. Still, I have done this before with messy laundry and STILL had to scrub it to get rid of trace smells.
I know this is all gross, but that's the special needs animal life, and I think it gives me some insight into what's really going on in our washing machines that others may not realize. This gives me hope that there could be evidence.
Sorry for the lengthy post and distasteful topic of nasty laundry.
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