Could be anything, even white blood cells attacking nothing, autoimmune, or something like an infection?
You need a doctor to run some urine tests to rule out problems. If no doctor available, a lab willing to do urine specimen tests without an order. Otherwise, a physician may know what it may or may not be from experience, testing only for the most necessary potential issues.
It could be anything like an infection, some tissue of the bladder, or protein in the urine (proteinuria) from infection (inflammation), high BP, or diabetes.