A renal transplant recipient 8 weeks post-transplant has rising creatinine. Urine PCR for BK polyomavirus is strongly positive. Plasma BK virus DNA quantification is ordered. Why is plasma DNAemia rather than viruria used to assess risk of BK virus nephropathy?
- A BK virus is never shed in urine of healthy transplant recipients
- B Viruria indicates active tubular replication that can occur without invasive disease, whereas sustained plasma DNAemia correlates with tissue-invasive nephropathy ✓
- C Plasma PCR is technically easier and cheaper than urine PCR
- D Urine PCR becomes negative once nephropathy is established
Correct answer: B. Viruria indicates active tubular replication that can occur without invasive disease, whereas sustained plasma DNAemia correlates with tissue-invasive nephropathy
Explanation
BK virus reactivation causes asymptomatic viruria in a large proportion of transplant recipients because the urothelium permits lytic shedding without invasive disease. Sustained plasma DNAemia reflects disseminated replication and correlates far better with biopsy-proven nephropathy, with levels persistently above roughly 10,000 copies/mL raising concern. Urine PCR does not disappear in nephropathy, it is simply less specific, and cost is not the deciding factor.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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