Background. BK virus (BKV)-associated nephropathy (BKVAN) has been increasingly recognized as an important cause of renal transplant dysfunction. We report the role of quantitative viral load monitoring in the management of BKVAN. Methods. We developed a real-time quantitative polymerase chain reaction (PCR) assay for BKV detection in urine and plasma. Four renal allograft recipients, including two children, with BKVAN were treated with low-dose cidofovir and followed prospectively. Results. The PCR assay showed a detection limit of 10 viral copies with an intra-assay coefficient of variation of 19%. All four patients with BKVAN demonstrated intranuclear inclusions on allograft biopsy and a progressive rise in serum creatinine; three patients underwent multiple biopsies before the diagnosis of BKVAN was made. Three of the patients experienced a "viral syndrome" before the onset of renal dysfunction. One child also demonstrated an echogenic renal mass. All of the patients demonstrated strongly positive urinary PCR values (> 100,000 copies/μL). BKV DNA was also detected in the plasma of three patients. All the patients were treated with intravenous low-dose cidofovir (0.25-1 mg/kg per dose, every 2-3 weeks, without probenecid). BK viruria resolved within 4 to 12 weeks (after 1-4 doses) of the cidofovir therapy, and all patients remain with stable renal function 6 to 26 months posttherapy. Conclusions. Quantitative PCR for BKV is a sensitive and reliable method for following the course of the infection in renal transplant patients. In addition, cidofovir therapy may be useful in the treatment of some of these patients, and its role needs to be investigated further.
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