Full myeloablative conditioning and an unrelated HLA mismatched donor increase the risk for BK virus-positive hemorrhagic cystitis in allogeneic hematopoetic stem cell transplanted patients.

BK virus (BKV)-associated hemorrhagic cystitis (HC), varying from mild hematuria with or without dysuria to life-threating bleeding and clots that may cause urinary obstruction and renal failure, causes significant morbidity and mortality in haematopoetic stem cell transplanted (HSCT) patients. Unfortunately, its development is difficult to predict since BK viruria is very common after HSCT and can be present in patients with and without HC. There is therefore the need to identify risk factors that may increase the risk of developing HC after HSCT. The viral load of BK-viruria, as well as BK viremia, has been monitored for this purpose. Moreover, having full myeoblative conditioning (MC) versus reduced intensity conditioning (RIC) prior to HSCT and an HLA-matched or -mismatched graft from an unrelated donor in contrast to an HLA-matched graft from a related donor have been studied as risk factors for HC. In addition, graft versus host disease has been examined, but has not been defined as a definite risk factor for HC. We conclude that the present evidence suggests that HSCT patients with BK viruria, receiving MC and an unrelated donor graft that is HLA-mismatched have an increased risk for developing HC in comparison to patients receiving RIC and an HLA-matched related donor graft.