OBJECTIVETo analyze the relationship between BK viruria and the late onset hemorrhagic cystitis (LOHC) after hematopoietic stem cell transplantation (HSCT), and investigate the role of BK virus load in the development of LOHC.

METHODSFrom August 2006 to April 2008, urine samples were collected weekly from 113 patients undergoing HSCT. Virus DNA were extracted from the urine samples and amplified by qualitative PCR. Real-time quantitative PCR was used to quantify BKV DNA in the urine samples of all BK viruria patients.

RESULTSLOHC occurred in 22 patients (19.5%), including grade 1 in 7, grade 2 in 11, grade 3 in 3, and grade 4 in one. The median onset time was 44 (13 - 114) days after transplantation. Twenty-one of which (95.5%) were BK virus positive, being significantly higher than that in non-LOHC patients (31.9%) (P = 0.000). No BK virus was detected in the healthy control group at the same time. Quantitative PCR detection showed that the mean BK virus DNA copies in LOHC patients at a week before occurring HC was higher than that at the first positive samples (10(5) copies/microl versus 10(4) copies/microl, P = 0.025), and it was no significant change at the onset and a week after HC. Meanwhile, there was no statistical difference in the mean level of BK virus DNA copies among the LOHC patients with different grades. The mean level of BK virus DNA copies in non-HC patients was 10(3) to 10(4) copies/microl, being lower than that in LOHC patients.

CONCLUSIONSBK viruria is an important pathogenic cause of the LOHC after HSCT. The occurrence of BKV viruria in HSCT patients, together with the increasing of BK virus DNA copies in urine, over the level of 10(5) copies/microl may indicate a possible development of LOHC.