BK virus nephritis: Risk factors, timing, and outcome in renal transplant recipients

Background. BK virus nephritis (BKVN) has emerged as an important cause of renal transplant failure. Quantified analysis of its timing and clinical course is generally lacking. We have thus quantified the timing, risk factors, evolution of renal function, and transplant graft outcome in renal transplant recipients with BKVN from our center. Methods. A total of 41 cases of BKVN were diagnosed in 1001 renal and renal/pancreas transplant recipients. There were 2 groups: group I (N=16), with diagnosis based on renal biopsy alone from January 1996 to August 2001, and group II (N=25), with diagnosis based on quantitative blood BKV-PCR and biopsy from September 2001 to December 2003. The demographics, the clinical course, immunosuppressive therapy, renal function, and graft outcome were quantified. Donor, recipient, and transplant risk variables were studied using a univariate analysis. Actuarial graft survival was calculated. An immunosuppressive scale created to evaluate the degree of immunosuppression in these patients and its reduction after the diagnosis of BKVN. Results. The median time from transplant to BKVN diagnosis was 318 days (range 48-1356). The actuarial graft survival in patients with BKVN at 6 months, 1, 3, and 5 years was 97%, 90%, 58%, and 47%. The corresponding values for those without BKVN were 94%, 92%, 83%, and 76%, respectively, P < 0.001. Graft loss occurred in 46% of patients. The rate of decline of renal function in group II (N= 25) patients in the 4 months preceding BKVN was rapid (4.8 mL/min/month) and this declined to 0.7 mL/min/month at 3 months' post-BKVN diagnosis, P=0.004. In those who recovered, the time to stabilization of renal function was a median of 112 days. The immunosuppressive scale score was 7 units at the time of diagnosis of BKVN and decreased to 3.5 units at 3 months' post-BKVN. Reduction in the dose of calcineurin inhibitors but not the overall reduction in dose of immunosuppression correlated with recovery of renal function in these patients. Conclusion. BKVN is a relatively late complication of renal transplantation. Despite reduction in immunosuppression, graft loss occurred in 46% of patients. There was a steep decline in renal function in months preceding the diagnosis of BKVN, and reduction in calcineurin inhibitor dose, but not overall immunosuppression, correlated with stabilization of renal function.