Decreased lymphocyte count before conditioning is associated with BK virus-associated hemorrhagic cystitis after allogeneic hematopoietic stem cell transplantation

•Haploidentical transplantation was a risk factor for BKV-HC.•Decreased lymphocyte count before conditioning was a risk factor for BKV-HC.•The occurrence of BKV-HC after allo-HSCT did not affect OS and PFS of the patients.•The severity of BKV-HC did not affect OS and PFS of the patients. BK virus-associated hemorrhagic cystitis (BKV-HC) is a serious complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT). It can cause morbidity and may increase treatment-related mortality. Previous studies showed that the occurrence of BKV-HC was related to various factors. However, there are still many controversial factors. It is not clear whether BKV-HC will affect the long-term prognosis of patients. We aimed to identify risk factors for BKV-HC after allo-HSCT and evaluate the effect of BKV-HC on overall survival (OS) and progression- free survival (PFS) of patients. We retrospectively analyzed the clinical data of 93 patients who underwent allo-HSCT. Univariate and multivariate analysis were used to identify risk factors for BKV-HC. The Kaplan-Meier method was used to estimate OS and PFS. A difference was considered statistically significant if P