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With a history of bladder cancer, that would be the first thing I'd think of.
Urinary infections can cause blood in the urine, but that's unlikely with no urinary symptoms.
Kidney stones can cause blood, but again there is usually pain.
Prostrate enlargement can sometimes cause blood in the urine.
Tumors of the bladder or kidneys could cause it.
Since you have an appointment for April 14 and you don't have pain or other symptoms, I would just keep your appointment. 3 or 4 days won't make any difference as far as diagnosis or treatment.
Your urologist will probably look into your bladder (cystoscopy) and then do further studies if the bladder looks clear. Best wishes.