Renal Transplant Recipient with Rising Creatinine and Fever
A 45-year-old woman with a living-related renal transplant 2 years ago presents with fever, malaise, and decreased urine output. Her baseline creatinine is 1.2 mg/dL, now 2.0 mg/dL. She is on tacrolimus, mycophenolate, and prednisone. Vital signs: temperature 38.5°C, BP 110/70, HR 100. Physical exam shows a tender transplant graft in the right iliac fossa. Labs: WBC 12,000, urine analysis with pyuria and bacteriuria, urine culture pending. Blood tacrolimus level is 8 ng/mL (target 5-10). Ultrasound shows mild hydronephrosis of the graft and a small perinephric fluid collection. The transplant team must decide on immediate management.
1. What is the differential diagnosis, and what immediate investigations and management are indicated?
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Differential diagnosis: 1) Acute graft pyelonephritis (most likely given fever, pyuria, bacteriuria, graft tenderness). 2) Acute rejection (can present with fever, graft tenderness, rising creatinine, but usually no pyuria). 3) Urinary tract obstruction (mild hydronephrosis on ultrasound). 4) Perinephric abscess or fluid collection (small collection noted). 5) Drug toxicity (tacrolimus level is therapeutic). 6) Viral infection (CMV, BK virus). Immediate investigations: Blood and urine cultures, CBC, electrolytes, renal function, tacrolimus level, CMV PCR, BK virus PCR, and blood gas. Imaging: Ultrasound with Doppler to assess vascularity and hydronephrosis; consider CT scan if abscess suspected. Management: 1) Admit for IV antibiotics (empiric coverage for gram-negative bacteria, e.g., ceftriaxone or piperacillin-tazobactam, adjusted to local resistance). 2) Fluid resuscitation. 3) Relieve obstruction if present: mild hydronephrosis may be due to infection/edema; if significant, place ureteral stent or nephrostomy. 4) Adjust immunosuppression: continue tacrolimus and mycophenolate but consider reducing mycophenolate if leukopenia; stress-dose steroids if septic. 5) Monitor urine output and creatinine. 6) If no improvement in 48-72h, consider graft biopsy to rule out rejection. 7) Surgical consultation for possible drainage of perinephric collection if abscess.
2. How would you differentiate between acute rejection and infection, and what is the role of graft biopsy?
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Differentiation: Infection typically presents with fever, graft tenderness, pyuria, bacteriuria, and positive cultures. Acute rejection may also cause fever and graft tenderness but usually lacks pyuria and bacteriuria; it may be associated with decreased urine output and rising creatinine. However, overlap exists. Blood cultures and urine cultures help. A rising creatinine despite antibiotics suggests rejection or obstruction. Ultrasound with Doppler may show increased resistive index in rejection, but not specific. The definitive test is graft biopsy. Role of biopsy: Indicated if the diagnosis is uncertain, if fever and graft dysfunction persist after 48-72 hours of appropriate antibiotics, or if rejection is suspected (e.g., no infection source, rising creatinine). Biopsy can show acute cellular rejection (tubulitis, interstitial inflammation) or antibody-mediated rejection (C4d staining). It also helps diagnose BK nephropathy or recurrent disease. Risks: bleeding, infection, graft loss (rare). In this patient, given clear evidence of urinary tract infection, initial management is antibiotics; if no improvement, biopsy. Also, BK virus PCR should be checked as it can mimic rejection.