Rising Creatinine and BK Viremia After Kidney Transplantation
A 47-year-old woman received a deceased-donor kidney transplant 8 months ago. Baseline creatinine was 1.2 mg/dL. Over 3 weeks, creatinine rises to 2.1 mg/dL. Tacrolimus trough is 10.5 ng/mL, mycophenolate 500 mg twice daily, prednisone 5 mg daily. BK viral load is 18,000 copies/mL; urine protein-to-creatinine ratio 0.4 g/g; urinalysis shows rare white cells and no casts. She is afebrile, BP 132/80 mmHg, and has no graft tenderness. Donor-specific antibodies are negative, complement is normal, and CMV viral load is undetectable. Ultrasound shows a normal resistive index and no hydronephrosis. The patient is reluctant to undergo another biopsy because a prior biopsy at 3 months showed no rejection. The nephrologist must decide whether to reduce immunosuppression empirically, obtain a biopsy, or treat for rejection.
1. What is the most likely diagnosis, and how does the biopsy change management?
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The leading diagnosis is BK virus nephropathy, but acute rejection remains possible and cannot be excluded by PCR alone. BK viremia above 10,000 copies/mL with rising creatinine is highly suspicious, but the absence of proteinuria and bland sediment do not rule out rejection. A biopsy with SV40 staining is the standard because management is opposite: BK nephropathy requires reduced immunosuppression, while rejection requires intensified therapy. Empirical reduction without biopsy risks missing rejection and losing the graft. The prior normal biopsy at 3 months does not cover the current episode. I would proceed with biopsy, including C4d and donor-specific antibody testing, and reduce mycophenolate only if the biopsy is delayed or the viral load is rising rapidly.
2. How would you monitor and prevent progression after diagnosis?
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If biopsy confirms BK nephropathy, reduce immunosuppression stepwise: lower tacrolimus trough to 5-8 ng/mL, reduce or stop mycophenolate, and consider switching to leflunomide or sirolimus. Do not give pulse steroids. Monitor BK viral load every 2-4 weeks until negative, along with creatinine. If the viral load does not fall, further reduce immunosuppression. If biopsy shows rejection, treat with steroids and optimize baseline immunosuppression. Screen urine and blood BK PCR monthly for the first 6-9 months and then every 3 months to 2 years. Avoid cidofovir unless under expert guidance because of nephrotoxicity.