Polyomavirus type BK (BKV) is a common DNA virus that may be latent within renal epithelial cells. Under certain circumstances it can cause a serious nephropathy in a transplanted kidney with the potential for allograft failure.


Risk factors:

(1) allograft from a seropositive donor to a seronegative recipient

(2) prolonged cold ischemia or ischemia-reperfusion injury

(3) multiple HLA mismatches between the donor and the recipient

(4) high doses of immunosuppressing drugs to control rejection, typically high dose corticosteroids, tacrolimus, mycophenolate mofetil or antilymphocyte antibodies


Clinical findings:

(1) ureteral ulceration with stenosis

(2) hemorrhagic cystitis

(3) improvement on reduction in immunosuppressive therapy


Laboratory findings:

(1) rising serum creatinine

(2) renal epithelial cells in the urine with nuclear viral inclusions ("decoy cells"; these are sensitive but not specific for the nephropathy)

(3) high plasma BKV viral load by DNA PCR (> 7,700 copies per mL)

(4) interstitial nephritis on allograft biopsy


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