Testing for polyomavirus type BK DNA in plasma to identify renal-allograftrecipients with viral nephropathy.

Background: Reactivation of polyomavirus type BK (BK virus) is increasingly recognized as a cause of severe renal-allograft dysfunction. Currently, pa tients at risk for nephropathy due to infection with the BK virus are ident ified by the presence of cells containing viral inclusion bodies ("decoy ce lls'') in the urine or by biopsy of allograft tissue. Methods: In a retrospective analysis, we performed polymerase-chain-reactio n assays for BK virus DNA in plasma samples from 9 renal-allograft recipien ts with BK virus nephropathy; 41 renal-allograft recipients who did not hav e signs of nephropathy, 16 of whom had decoy cells in the urine; and as imm unocompromised controls, 17 patients who had human immunodeficiency virus t ype 1 (HIV-1) infection (stage C3 according to the classification of the Ce nters for Disease Control and Prevention) and who had not undergone transpl antation. Results: In all nine patients with BK virus nephropathy, BK virus DNA was d etected in the plasma at the time of the initial histologic diagnosis (a me an [+/-SD] of 46+/-28 weeks after transplantation) and during the course of histologically diagnosed, persistent BK virus disease. In three of the six patients with nephropathy who were studied serially after transplantation, BK virus DNA was initially undetectable but was detected 16 to 33 weeks be fore nephropathy became clinically evident and was confirmed by biopsy. Tes ts for BK virus DNA in plasma became negative and the nephropathy resolved after the doses of immunosuppressive drugs were decreased in two patients a nd after removal of the renal allograft in three patients. BK virus DNA was found in the plasma of only 2 of the 41 renal-allograft recipients who had no signs of nephropathy and in none of the patients with HIV-1 infection. Conclusions: Testing for BK virus DNA in plasma from renal-allograft recipi ents with use of the polymerase chain reaction is a sensitive and specific method for identifying viral nephropathy. (N Engl J Med 2000;342:1309-15.) (C) 2000, Massachusetts Medical Society.