[Urinary cytology after renal transplantation]

BK polyomavirusnephropathy (BKN) is a serious complication of the potent immunosuppressive therapies in renal allograft recipients. BKN occurs in 5% of the patients and leads to allograft loss in approximately 50% of those affected. Early detection of BKN improves the chances to retain the allograft by allowing immediate intervention. Urine cytology is a simple, cheap and reliable method for early identification of patients at risk for BKN, together with BK DNA analysis in the serum. BK virus causes a spectrum of morphologic changes of tubular and urothelial cells that can be viewed online at http://vmic.unibas.ch/patho/seminar/index.html. These BK infected cells are called "decoy cells" as they can mimic the features of bladder carcinoma cells. In addition, certain morphologic features of the urinary sediment including tubular cells and lymphocytes can anticipate renal rejection. Historically, urinary cytology was important to screen patients with allograft for analgetic nephropathy for malignant cells, since they were at greatly increased risk of urothelial carcinoma.