Blood in urine, also known as hematuria, occurs when red blood cells are present in the urine. Normally, urine should not contain blood, or it may only have trace amounts that are undetectable without specific tests. When blood is detected, it can either be visible to the naked eye (called gross hematuria) or only detectable under a microscope or with dipstick tests (microscopic hematuria).
Testing for blood in urine can reveal important information about the health of the urinary system, including the kidneys, bladder, ureters, and urethra.