We just recently had a discussion about this because normally red urine does not mean blood, there is sort of a dark rusty red that can happen with diet, extra A in the diet, antibiotics, even weather changes. Real blood is normally very bright bright red. But having a bunny who DID pee blood, I do know it can happen. In my case, my bunny Jack had a large bladder stone and when he got alot of exercise, it would scrape against the bladder wall and cause him to pee out bright red blood. The difference between the the red urine and blood was that they would dry differently. The urine would dry about the same color, where the blood dried just like blood does – turns from bright red, to dark red/brown.
The other thing that I took notice of was that when I sprayed hydrogen peroxide on the blood, it would foam up alot, where it wouldn’t do that with just urine.
I’m going to try and get the link to the photos that were posted by Jersey in the thread about this – it had photos of red urine and the blood. It may be helpful. Okay here is the link –
https://binkybunny.com/FORUM/tabid/54/aff/2/aft/105265/afv/topic/afpgj/2/Default.aspx 
(go to page 2)