Kidney Transplant Patient with Rising Creatinine
A 45-year-old woman with a kidney transplant 2 years ago presents with fever and malaise. Her baseline creatinine is 1.2 mg/dL. Current labs: creatinine 2.0 mg/dL, tacrolimus trough 12 ng/mL (target 5-8), BK viral load 10,000 copies/mL, urinalysis with 10-20 WBCs and rare decoy cells. She is on tacrolimus, mycophenolate, and prednisone. She has a history of CMV infection. She reports no missed medications.
1. What is the differential diagnosis and what initial tests would you order?
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Differential: acute rejection (cellular or antibody-mediated), BK virus nephropathy, drug toxicity (tacrolimus), infection (CMV, urinary tract infection), obstruction, recurrent glomerulonephritis. Initial tests: urine culture, CMV PCR, BK viral load (already 10,000), renal ultrasound to rule out obstruction, and consider allograft biopsy. Also, check tacrolimus level (12, high). The presence of decoy cells and BK viremia suggests BK nephropathy. However, high tacrolimus level could cause toxicity. So order: renal ultrasound, urine culture, CMV PCR, and biopsy. Also, check donor-specific antibodies (DSA) to rule out antibody-mediated rejection.
2. If biopsy shows BK virus nephropathy, how would you manage it?
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Management of BK virus nephropathy: reduce immunosuppression. The mainstay is to decrease immunosuppression to allow immune clearance. Typically, reduce tacrolimus trough to <6 ng/mL or switch to mTOR inhibitor? Also, reduce mycophenolate dose or stop it. Consider leflunomide or cidofovir as adjunctive therapy, but evidence is limited. Monitor BK viral load every 2-4 weeks. If no improvement, consider IVIG or other therapies. Also, check for graft dysfunction. So: reduce immunosuppression (decrease tacrolimus and mycophenolate), monitor BK viral load, and consider leflunomide.