Analytical and clinical performance characteristics of the Simplexa BK virus quantitative PCR assay for the diagnosis of polyomavirus-associated nephropathy in renal transplant recipients using plasma and urine specimens.

BACKGROUND: Polyomavirus-associated nephropathy is a significant cause of kidney rejection in renal transplant recipients. Quantification of BK viral load in plasma and urine can predict the development of polyomavirus-associated nephropathy, though each assay requires careful evaluation of analytical and clinical performance characteristics for optimal use.
OBJECTIVES: This study evaluated the analytical and clinical performance characteristics of the Simplexa BK virus quantitative PCR assay. STUDY
DESIGN: Analytical validation was performed using commercial standards, BK virus stock culture, and patient specimens. Clinical performance was evaluated using biopsy-proven BK nephropathy as the gold standard.
RESULTS: The Simplexa BK virus quantitative PCR assay was linear over a range of 2.7-10.4 log(10) copies/mL. Limit of detection was 2.7-2.8 log(10) copies/mL in plasma and urine samples. Sensitivities were 100% and 100% and specificities were 84% and 86% for plasma and urine samples, respectively, when compared to a reference BK assay. Clinical cutoff values of 4.0 log(10) copies/mL (plasma) and 7.5 log(10) copies/mL (urine) yielded 100% sensitivity and specificities of 87.5% and 85%, respectively, for biopsy-proven polyomavirus nephropathy.
CONCLUSIONS: The Simplexa BK virus quantitative PCR assay has high sensitivity and acceptable analytical characteristics for clinical use. The clinical cutoff values presented here provide a rational approach to the monitoring and treatment of renal transplant recipients for polyomavirus-associated nephropathy.