[Clinical diagnosis and treatment of BK virus infection in renal transplant recipients].

OBJECTIVE: To explore methods of clinical diagnosis and treatment of BK virus (BKV) infection in renal transplant recipients. METHODS: Urine samples were collected from 227 renal transplant recipients who had undergone renal transplantation at most 48 months to detect the decoy cells. Samples of urine and peripheral blood (BP) were collected to undergo real-time PCR to detect the BKV DNA. Part of the renal-recipients received graft biopsy. The recipients with BKV viruria or viremia were divided into 2 groups: intervention group and control group. The 51 patients of the intervention group had the doses of cyclosporine A (CsA) reduced (n=19), had their doses of FK506 reduced (n=22), or underwent replacement of FK506 with CsA (n=10). And other 29 patients in the control group did not receive any intervention. Acute rejection was intensively monitored. The amount of decoy cells, and BKV load in the urine and PB samples were measured again after 3 months. RESULTS: The positive rates of urine decoy cell, BKV viruria, and viremia in all patients were 33.0%, 33.5%, and 15.4% respectively. In the intervention group, the median levels of decoy cells in urine, and of BKV DNA in urine and PB before intervention were 5.0/10 HP, 1.50 x 10(4) copies/ml and 0 copy/ml respectively ; and the median levels of decoy cell in urine, and of BKV DNA in urine and PB were all 0 after intervention, all significantly lower than those before intervention (all P < 0.01). In the control group, the median levels of decoy cells in urine, and of BKV DNA in urine and PB were 6.0 /10 HP, 0.79 x 10(4) copies/ml, and 0 copy/ml respectively before observation, and the median level of BKV load in urine ofter observation was 2.21 x 10(4) copies/m, significantly higher than that before observation (P < 0.01), however, the median levels of decoy cells in urine and of BKV DNA in PB were 5.0 /10 HP and 0 copy/ml respectively, not significantly different from those before observation ( both P > 0.05). The differences between the levels of urine decoy cells, urine BKV DNA level and blood BKV DNA level of the intervention group were all significantly greater than those of the control group (Z = -2.749, -5.089, -1.996; P = 0.006, 0.000, 0.046 respectively). And during the intervention no acute rejection was observed. Four cases of BKVAN were diagnosed. Treatment of immunosuppression reduction showed effectiveness in 4 BKVAN recipients. The levels of decoy cells in urine, and BKV load in urine and in PB samples were all decreased. The graft functions were improved. CONCLUSION: Urine cytology is very convenient, useful and sensitive for the evaluation and followup of renal transplant patients, and can reflect renal histological presentation indirectly. Also BKV DNA detection in the urine and peripheral blood is important to screen the evidence of BK reaction in order to prevent irreversible graft damage of BKVAN. The treatment of immunosuppressant reduction and replacement of FK506 with CsA are effective in BKV infection recipients at the early stage.