A family member of a patient who has returned to the special unit after renal transplantation is alarmed by blood in the urine of the patient. What is the nurse's best explanation when explaining the reason for hematuria in this patient?

It is related to the immunosuppressant drugs taken before transplantation.

It is a normal postoperative expectation.

It is caused by dye injected during surgery.

It is caused by a small vessel that may be bleeding but will coagulate as urine flow increases.