Test ID: QBKU    
BK Virus, Molecular Detection, Quantitative, PCR, Urine

A prospective and diagnostic marker for the development of BK virus nephropathy in renal transplant recipients

This test should not be used to screen healthy patients. Depending on the population, varying percentages of patients may be found to be positive.

Polyomaviruses are small (45 nm, approximately 5000 bp), DNA-containing viruses and include 3 closely related viruses of clinical significance; 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, and among those patients the average time from transplant to diagnosis is about 40 weeks (range 6-150).(3) Polymerase chain reaction 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) However, BKV DNA is typically detectable in urine prior to plasma and may serve as an indication of impending BKVAN. Viral loads of greater than 32,000 IU/mL in urine may also indicate a risk for BKVAN. Serial monitoring of viral loads may be indicated to assess changing levels of BKV DNA.

None detected

Increasing copy levels of BK virus (BKV) DNA in serial specimens may indicate possible BKV-associated nephropathy (BKVAN) in kidney transplant patients.

Viral loads of above 32,000 IU/mL in urine may also indicate a risk for BKVAN.

This assay does not cross react with other polyomaviruses, including JC virus and SV-40.

No significant cautionary statements

The following validation supports the use of this assay for clinical testing.

Accuracy/Diagnostic Sensitivity and Specificity:

Results from this real-time polymerase chain reaction (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 specimens had low viral DNA copy numbers (<5000 copies/mL), which is associated with greater variability of quantitative results.

Supplemental Data (Spiking Studies):

To supplement the above data, 30 negative plasma and urine specimens were spiked with BK virus (BKV)-positive control plasmid at the approximate 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.

Analytical Sensitivity/LOD:

The lower LOD of this assay is 5000 DNA target copies per mL in urine and plasma (1600 IU/mL).

Analytical Specificity:

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.

Precision:

Qualitative inter-assay and intra-assay precision were 100%. Quantitative values had a standard deviation of <0.25 log10 across the analytical measuring range.

Reference Range:

The reference range of BKV in plasma is "None Detected." This test is not to be used to screen healthy patients. It is to be used for patients with a clinical history or risk factors for BKV-associated nephropathy.

Reportable Range (lower and upper limits of quantification, analytical measurement range):

Reportable range is from 1600 to 16,000,000 IU/mL.

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 Transplantation. 2002;2(5):481

3. Hirsch HH: Polyomavirus BK Nephropathy: A (Re-)emerging complication in renal transplantation. Am J Transplantation. 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