system
Given the following post, respond as if you're commenting on Reddit:
human
Is there such a thing as excess blood in your system? Hypothetically speaking what would happen to someone if you gave them a rapid blood transfusion when they didn't need one thus filling them up with more blood than they need?

I was watching a youtube let's play and after getting hit real bad one of the commentators said it was fine, they had too much blood anyway. While obviously a joke it got me curious what would happen if that were a real thing.
gpt
So this can happen. It's called Transfusion Associated Circulatory Overload. Part of the pathology is essentially excess fluid leaking out into the tissues, such as the lungs. Younger, healthier people with fully functioning hearts and kidneys are more able to deal with the excess fluid, so it's less likely to happen in this group.

In theory if you could give just the red blood cells, taking away some of the fluid component, you'd been causing the viscosity of the blood to go up. This predisposes to blood clots, strokes, etc.