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Rapid detection of BK virus DNA
Polyomaviruses are small (45 nm, approximately 5,000 base pairs), DNA-containing viruses and include 3 closely related viruses of clinical significance, Simian virus 40 (SV-40), JC virus (JCV), and BK virus (BKV). SV-40 naturally infects rhesus monkeys but can infect humans, while BKV and JCV cause productive infection only in humans.(1,2) Acquisition of BKV begins in infancy. Serological evidence of infection by BKV is present in 37% of individuals by 5 years of age and over 80% of adolescents.
BKV is an important cause of interstitial nephritis and associated nephropathy (BKVAN) in recipients of kidney transplants. Up to 5% of renal allograft recipients can be affected about 40 weeks (range 6-150) post-transplantation.(3) PCR analysis of BKV DNA in the plasma is the most widely used blood test for the laboratory diagnosis of BKV-associated nephropathy. Importantly, the presence of BKV DNA in blood reflects the dynamics of the disease: the conversion of plasma from negative to positive for BKV DNA after transplantation, the presence of DNA in plasma in conjunction with the persistence of nephropathy, and its disappearance from plasma after the reduction of immunosuppressive therapy.(4-8) Viral loads of >10,000 copies/mL in plasma may indicate a risk for BKVAN (see QBK / BK Virus, Molecular Detection, Quantitative, PCR, Plasma).
Results of plasma tests are reported in terms of the presence or absence of BK virus (BKV).
Detection of BKV DNA in clinical specimens may support the clinical diagnosis of renal or urologic disease due to BKV. Correlation of qualitative results with clinical presentation and BK viral load in urine and/or plasma is recommended.
A negative result does not rule out the possibility of BK virus (BKV) infection.
This assay is only to be used in patients with appropriate risk factors for BKV-associated disease and is not indicated for screening of asymptomatic patients.
The following validation supports the use of this assay for clinical testing.
Accuracy/Diagnostic Sensitivity and Specificity:
Results from this real-time PCR assay on the LightCycler (LC PCR) were compared to a previous PCR assay (directed to VP2 region of the polyoma virus based on a published method) on 112 plasma specimens and 108 urine specimens. Using the previous method as the gold standard, the diagnostic sensitivity and specificity is 94% and 90% for plasma and 100% and 100% for urine, respectively. The discrepant samples had low viral DNA copy numbers (<5,000 copies/mL) and may not have been reproducible.
Supplemental Data (Spiking Studies):
To supplement the above data, 30 negative plasma and urine specimens were spiked with BK virus (BKV)-positive control plasmid near the limit of detection (LoD). The 30-spiked specimens were run in a blinded manner along with 57 plasma and 58 urine negative (nonspiked) specimens. 100% of the spiked specimens were positive and 100% of the nonspiked specimens were negative.
The LoD of this assay is 244 DNA target copies per mL in urine and plasma.
No PCR signal was obtained from the extracts of a variety of human viruses that can be found in urine or plasma, including cytomegalovirus, Epstein-Barr virus, human herpesvirus-6, enterovirus, adenovirus, and mumps virus.
Inter-assay precision was 100% and intra-assay precision was 100%.
The reference range of BKV in plasma is negative.
In renal transplant patients, plasma viral load copies of >10,000 copies/mL may indicate increased risk of BKV disease. Therefore, a quantitative test may be appropriate in this population (see QBK / BK Virus, Molecular Detection, Quantitative, PCR, Plasma).
This is a qualitative assay and the results are reported as negative or positive for targeted BKV.
1. Kazory A, Ducloux D: Renal transplantation and polyomavirus infection: recent clinical facts and controversies. Transplant Infect Dis 2003;5(2):65
2. Vilchez RA, Arrington AS, Butel JS: Polyomaviruses in kidney transplant recipients. Am J Transplant 2002;2(5):481
3. Hirsch HH: Polyomavirus BK nephropathy: a (re-)emerging complication in renal transplantation. Am J Transplant 2002;2(1):25-30
4. Randhawa PS, Demetris AJ: Nephropathy due to polyomavirus type BK. N Engl J Med 2000;342:1361-1363
5. Volker NT, Klimkait IF, Binet P, et al: Testing for polyomavirus type BK DNA in plasma to identify renal-allograft recipients with viral nephropathy. N Engl J Med 2000;342:1309-1315
6. Hariharan S: BK virus nephritis after renal transplantation. Kidney Int 2006;69:655-662
7. Blanckaert K, De Vriese AS: Current recommendations for diagnosis and management of polyoma BK virus nephropathy in renal transplant recipients. Nephrol Dial Transplant 2006;21(12):3364-3367
8. Viscount HB, Eid AJ, Espy MJ, et al: Polyomavirus polymerase chain reaction as a surrogate marker of polyomavirus-associated nephropathy. Transplantation 2007;84(3):340-345