Look at Constantine over here, cursed to live.

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Piss is blood, in a sense. It's the bits of your blood that get sieved out and rejected by your kidneys.

Normally those are the only bits supposed to be getting out. But if the filter is busted (kidney trouble) or if the walls of the storage tank it sits in after filtering become damaged (bladder trouble), you can end up pissing actual, unfiltered blood.

Alternatively, you ate something recently with a strong red pigment that can survive digestion, enter the bloodstream, get strained out by the kidneys, and collect in your piss in high enough concentration to turn it red. Beets are a pretty famous culprit.

Yeah, bladder cancer.

Not only bladder cancer but a whole bunch of things. I used to run home from work and I would always pee right beforehand so I wouldn't risk having to find some sort of place to pee, but then I started peeing blood every couple of weeks when my mileage went up to around the 10 mile mark. Apparently hematuria can happen from basically having a totally empty bladder chafe itself raw if you run long enough lol. I quit peeing before leaving work after my doctor recommended giving that a shot and it cleared up

yes though normally pee is brown/red from myoglobin accumulation (muscle breakdown) which is a sign of many things, some of them normally fine but many are extremely life threatening, and can lead to kidney failure. if your pee is ever brown or red you should most likely see a healthcare professional and have them do a urinalysis.

Yep. Kidney stones can make anything coming out of your urethra bloody. And holy hell does pissing blood that way hurt.

Yes, even for some minor things. I once got a UTI and didn't get it checked out for a week (I was mega dumb back then). What pushed me eventually to get a doctor to see me was when I started pissing blood. Not loads, but even a single drop was enough to spook me. Got some antibiotics and all was back to normal in a couple days.