Urinary tract infections, kidney infections, and kidney or bladder stones are potential causes of blood in urine, indicates Mayo Clinic. Other causes for bleeding of the bladder include cancer, kidney disease, an enlarged prostate, inherited disorders and injuries. Some medications, injuries and strenuous exercise can also cause bleeding in a person's bladder.
Hematuria causes kidneys or other parts of the urinary tract to let blood cells leak into urine, explains Mayo Clinic. Urinary tract infections can be the origin of such leaking. UTIs occur when bacteria from the large intestine go into the anus, and then spread to the urethra, explains WebMD. Once in the urethra, the bacteria migrates to the bladder, leading to a UTI and possibly kidney infection. Sex can also bring bacteria into the urinary tract. For some people, especially older adults, the only symptom of a UTI can be barely detectable blood in urine.
Minerals in nondiluted urine can leak out, thus forming into crystals on the walls of a person's bladder or kidneys, states Mayo Clinic. The crystals can manifest into small, hard stones that may lead to debilitating pain and bleeding, particularly when the stone is being passed through the urethra.
Often in middle age, the prostate gland enlarges, states Mayo Clinic. As it grows, it pushes on the urethra and partially blocks the flow of urine. An infection in the prostate can result in visible and microscopic bleeding in urine.