There are two main causes ofhemorrhagic cystitis in the transplant patient: conditioning regimen-relatedtoxicity and viral infection. Cystitis that occurs early (days 1 to 14) isusually caused by the conditioning agents, and is generally related tohigh-dose cyclophosphamide. The incidence of early cystitis is reduced withthe use of aggressive hydration with forced saline diuresis or theadministration of mesna for uroprotection. Mesna binds to an inactivemetabolite of cyclophosphamide, acrolein, preventing urothelialinflammation. Mesna is effective only during cyclophosphamidemetabolism/excretion, but not once hemorrhagic cystitis is established. Werecommend prehydration with 1000 mL of D5NS with 20 mEq/L of KCl at 500 mL/hfor at least 2 hours before cyclophosphamide, and maintenance of hydrationwith D5NS at 200 mL/h for 12 hours after cyclophosphamide using furosemideif necessary to maintain urine output >200 mL/h.

Hemorrhagic cystitis occurringafter day 14 is usually due to a viral infection, the two most common beingBK virus and adenovirus.