Rising Creatinine and BK Viraemia After Kidney Transplantation
A 48-year-old man received a deceased-donor kidney transplant eight months ago. His baseline creatinine was 130 µmol/L, but it has risen to 210 µmol/L over three weeks. He feels well and has no fever, dysuria or graft tenderness. Ultrasound shows normal graft echogenicity and no hydronephrosis; Doppler indices are normal. Tacrolimus trough level is 6 ng/mL, and he takes mycophenolate and prednisolone. Donor-specific antibodies are negative. BK virus PCR in plasma is 12,000 copies/mL. Urine culture is negative. He has no history of non-adherence, and his only new medication was a course of antibiotics for a chest infection two months ago. The transplant team is considering empirical treatment for acute rejection with methylprednisolone while awaiting biopsy. The patient is anxious and asks whether reducing immunosuppression will cause rejection.
1. What is the differential diagnosis and how would you investigate it? Include the role of biopsy.
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The main differential is BK virus-associated nephropathy, acute cellular rejection, calcineurin inhibitor toxicity, recurrent or de novo glomerulonephritis, and less likely urinary obstruction or infection, which the ultrasound and urine culture have largely excluded. A rising creatinine with BK viraemia is not enough to diagnose BK nephropathy, because BK viraemia can coexist with rejection. I would arrange an urgent graft biopsy with light microscopy, SV40 staining for BK virus and C4d staining, and check donor-specific antibodies again. I would also quantify BK viral load and repeat it, check tacrolimus levels and review medications. Empirical methylprednisolone before biopsy is risky: if this is BK nephropathy, increasing immunosuppression can worsen viral injury. Biopsy should be done within 24–48 hours. If biopsy cannot be performed promptly and the patient is stable, I would still avoid blind steroid pulses and discuss the case with the transplant team.
2. How would you manage the BK viraemia and immunosuppression while awaiting biopsy results?
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While awaiting biopsy, I would reduce immunosuppression cautiously rather than stopping it. A common approach is to reduce the antimetabolite, mycophenolate, by about 30–50% and keep tacrolimus at a therapeutic level, with close monitoring of renal function and BK viral load every 1–2 weeks. I would not start empirical steroids for rejection. If biopsy confirms BK nephropathy, further reduction of the calcineurin inhibitor may be needed, with a switch to an mTOR inhibitor considered in selected patients, although evidence is limited. If biopsy shows rejection, immunosuppression is increased and BK viraemia is monitored. I would avoid routine fluoroquinolone prophylaxis for BK, and I would not use cidofovir or leflunomide as first-line therapy. The patient needs to understand that the balance is dynamic and that reducing immunosuppression is itself a treatment for BK.
3. What would you tell the patient about the balance between rejection and BK virus?
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I would explain that his kidney function has worsened and that there are two main possibilities: rejection, which needs more immunosuppression, or BK virus injury, which needs less. Because the treatments pull in opposite directions, a biopsy is essential rather than guessing. I would reassure him that reducing one medication slightly is not the same as stopping all immunosuppression, and that we will monitor his kidney function and virus levels closely. I would be honest that BK virus can cause scarring and that early reduction of immunosuppression gives the best chance of preserving the graft. If rejection is found, we will treat it and then rebalance his medications. I would also explain that he should report fever, reduced urine output, graft pain or new symptoms immediately, and that he needs regular blood tests.