Heavy exercise, certain foods (e.g. food colouring, beetroot, carrots), kidney stones, menstrual periods, and urine infections can cause blood in the urine. Blood can be noticed by the person (macroscopic) or require urine analysis (microscopic).
Some autoimmune kidney diseases can also cause blood in the urine due damaged filtering units (glomeruli) in the kidneys. Rarely, there are some diseases that are genetic/hereditary that could be the underlying cause.