Background: Quantification of the serum level of BK virus is used as a surrogate marker for the early onset of BK virus nephropathy. However, little is known about the diagnostic value of the urine level of BK virus for nephropathy or the relationship between the serum and urine viral load. We investigated the correlation between urine and serum BK virus levels after renal transplantation.
Methods: From November 2008 to August 2013, a total of 270 renal transplant patients who were followed at our institution were included in this study. Urine and serum were collected simultaneously. BK virus levels were quantified in 894 urine and serum samples using a real-time polymerase chain reaction assay.
Results: BK virus was detected in 178 urine samples and 36 serum samples. Among the BK virus-positive urine subjects, the positive predictive value for viral detection in the serum was 9% (13/147) when the urinary virus level was <10(7) copies/mL and 74% (23/31) when the urinary virus was ≥ 10(7) copies/mL. Serum BK viral levels were ∼2-3 log units lower than those in urine.
Conclusions: BK virus was detected more frequently in serum when present in urine at ≥ 10(7) copies/mL after renal transplantation.
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