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Assay Sheet

Test ID Code

2300 BKV IgG Antibody

CPT Code

86790

Clinical Utility

Determining the level of anti-BKV IgG antibodies in both kidney donor and recipient has been reported to be a possible factor in predicting the risk of BK nephropathy, an important cause of allograft dysfunction. Moreover, recent scientific data has shown that BK nephropathy in pediatric kidney recipients is associated with the recipients’ BKV seronegativity pre-transplant, indicating a potential need for pre-transplant BKV serological testing.

Procedure

Indirect Enzyme-Linked Immunosorbent Assay (ELISA)

Specimen type & specimen handling

Whole Blood: 4 to 5 ml collected in EDTA (lavender top) tube. Do not freeze; ship ambient. Testing will be performed on plasma separated from the submitted whole blood specimen. Whole blood specimens are accepted as a matter of convenience for the originating laboratory. 

Plasma: Collect 4-5 mls whole blood in EDTA or ACD tube, centrifuge and transfer 2 mls plasma to sterile, screw top tube. Ship at ambient temperature Monday thru Friday. Specimen must be received within 96 hrs of collection.

Serum: Collect 4-5 mls whole blood in red top tube, centrifuge and transfer 2 mls serum to sterile, screw top tube. Ship at ambient temperature Monday thru Friday. Specimen must be received within 96 hrs of collection.

Causes for Rejection

Call ViraCor at 800-305-5198 if specimen is greater than 96 hrs old.

Specificity

The ELISA detects human IgG antibodies to the BKV VP1 protein.

Assay Range

Antibody Titers from <40 to >163840 Test results are reported as an antibody titer, which is the inverse of the specimen dilution that produces signal greater than the assay background level (e.g. 1:2560 specimen dilution is reported as 2560).

Turnaround Time

1 to 7 business days from receipt of specimen; assay performed weekly on Wednesdays

Shipping

The CPT codes provided are based on ViraCor’s interpretation of the American Medical Association’s Current Procedural Terminology (CPT) codes and are provided for informational purposes only. CPT coding is the sole responsibility of the billing party. Questions regarding coding should be addressed to your local Medicare carrier. ViraCor assumes no responsibility for billing errors due to reliance on the CPT codes illustrated in this material. The BKV IgG Antibody test is performed pursuant to a licensed agreement with the National Institutes of Health.This assay was developed and the performance characteristics were determined at ViraCor Laboratories. This test is performed in a CLIA certified laboratory. FDA approval is not required for the performance of this test.

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Pathogen Overview

ABOUT BK VIRUS

BK is a member of the Polyomaviridae family, which are small, nonenveloped viruses with a closed, circular double-stranded DNA genome. Polyomaviruses are ubiquitous in nature and can be isolated from a number of species. BKV and JCV make up the members of the human polyomaviruses. BK virus was first isolated in 1971 from the urine of a renal transplant patient who developed ureteral stenosis postoperatively. The virus was named after the initials of this first patient. Primary infection with BKV typically occurs in childhood, probably as a mild upper respiratory infection. Studies suggest over 90% of the population has been infected with BK virus by the age of 10 years. Following primary infection, the virus establishes latency in the urogenital tract where it remains for life. Reactivation of the virus can occur spontaneously or, more commonly, in an immunocompromised host.

BK VIRUS CLINICAL MANIFESTATIONS

BK virus associated renal allograft nephropathy (BKVAN) has emerged as a major cause of renal allograft dysfunction worldwide since the early 1990s. This emergence seems to have coincided with the widespread availability of potent immunosuppressive drugs. BKVAN can be a difficult clinical problem with a prevalence rate of 1 tp 10% and a graft loss rate of 10 to 80%, depending on the center’s BK screening program and use of immunosuppression.

In renal allograft recipients, BK reactivation most frequently manifests itself as a nephropathy. However, in hematopoietic stem cell transplant (HSCT) patients, hemorrhagic cystitis is frequently seen. Less common presentations of BKV reactivation include echogenic mass, interstitial nephritis, and ureteric stenosis. Pediatric renal transplant patients who are seronegative at the time of transplantation seem to be at particularly high risk of BKVAN, although this requires further study for confirmation. These patients may present with a viral prodrome consisting of low grade fever, myalgia, and mild gastroenteritis prior to onset of allograft dysfunction.

Despite recent advances in BK diagnostics, it remains unclear why only a small number of renal transplant patients, the majority of whom are seropositive for BKV, develop full blown renal disease. Several efforts have been made to identify risk factors for development of BKVAN. Specific immunosuppressive agents, such as tacrolimus and mycophenolate mofetil (MMF), are generally believed to be associated with a higher incidence of BKVAN. However, BKVAN has been observed with all immunosuppressive regimens. It may be more plausible that patients whose immunosuppression is maintained at a higher total level, rather than with a specific agent, have an increased incidence of BKVAN. Other risk factors that have been associated with an increased risk of BKVAN include HLA mismatch, the use of corticosteroid pulses to treat graft rejection, cell injury due to acute rejection or cold ischemia, male gender, and BKV serology. However, many other studies have contradicted these associations. Recently, host and viral genomic variation has also been correlated with development of BKVAN. DNA sequence variations in several putative transcription factor binding sites in the noncoding control region (NCCR) of the BK genome and polymorphisms of several cytokine genes have been proposed to play a role in the pathogenesis of BKVAN. The effect of mutations within the BKV genome on therapy outcome is unknown at this time. It seems that BKVAN is promoted by the concurrent presence of several risk factors, among which immunosuppression appears to be a prerequisite.

BK VIRUS LABORATORY DIAGNOSIS

The key to confirming the diagnosis of BKVAN remains the recognition of BKV inclusions in tubular and glomerular epithelial cells in renal allograft biopsy specimens. Viral inclusions in BKVAN are often associated with variable mononuclear interstitial infiltrates and focal tubulitis, which closely resembles acute rejection. Because of the focal nature of BKV replication in the kidney, negative biopsy results cannot rule out BKVAN. Interestingly, the diagnosis of BKVAN is often preceded by a diagnosis of acute rejection episode(s) in many patients. These episodes are, or tend to gradually become, nonresponsive to conventional therapy. It is unclear if these rejection episodes may be early stages of BKVAN, prior to the viral inclusions becoming conspicuous on biopsy. Thus, a high index of suspicion is needed for diagnosis of BKVAN, especially in patients who present an unexplained rise in serum creatinine or have episodes of acute rejection that are refractory to steroid therapy.

Molecular detection methods, such as real-time polymerase chain reaction (PCR), provide a sensitive and noninvasive means to detect BKV in urine and blood. Molecular detection of BKV allows patients to be placed on a regular monitoring program that allows detection of the virus prior to development of nephropathy (and therefore kidney damage). There are numerous studies in the literature demonstrating rising BK urinary loads, by real-time, quantitative PCR, prior to presentation with full blown BKVAN. Such a scenario can often predict and predate BKVAN by several weeks to several months. Urinary viral load of more than 10,000,000 copies/ml has now been proposed to be a significant risk factor for BKVAN. A rising titer of several log orders can also be of clinical significance. Besides the role of urinary BKV viral load in BKVAN management, especially in early stages, real-time PCR analysis of blood samples to detect and quantify BKV DNA is rapidly becoming the test of choice for confirming diagnosis and monitoring progression of active BKVAN. The sensitivity of DNA PCR is considered to be 100% and the specificity approximately 85%. The interdisciplinary panel of BKV experts that met in Basel, Switzerland in October 2003 proposed a titer of > 10,000 copies/ml in plasma (or serum) to be a significant marker of BKVAN with a specificity of =93%. The panel recommended renal allograft recipients be screened for BKV replication in the urine every 3 months for the first 2 years following transplant and annually thereafter until the fifth year post-transplant, in addition to performing urinary screening whenever an allograft biopsy is performed, whether it be for allograft dysfunction or surveillance biopsy.

To view the panel’s recommendation in further detail access: Transplantation; Volume 79, Number 10, May 27, 2005.

BK VIRUS TREATMENT

Although various therapeutic strategies have been tried for BKVAN, the results are variable with graft loss rate ranging from 10 to 80%. In most centers, BKVAN is initially treated by lowering immunosuppression and sometimes additionally by discontinuing drug regimens containing tacrolimus. These therapeutic attempts can result in good clinical success if BKVAN is diagnosed during an early stage, thus emphasizing the need for regular monitoring. Several centers have reported significantly improved graft survival rates upon initiation of a monitoring program. If lowering of immunosuppression does not result in resolution of nephropathy, a consideration for the institution of additional therapy should be made in an expeditious manner. Currently, specific antiviral strategies for BKVAN are poorly defined, although low dose cidofovir (0.25-1 mg/kg without probenecid) has been successful in a number of cases. Additionally, there have been reports of successful use of leflunomide in resolving BKVAN.

CONCLUSION

There remains much to be learned regarding BK risk factors, both viral and recipient, as well as in treatment and prevention strategies. There is a critical need for development of antiviral drugs that will inhibit the replication of BK virus.

Selected References

Hirsch HH, Brennan DC, Drachenburg CB, et al. Polyomavirus-associated nephropathy in renal transplantation: interdisciplinary analyses and recommendations. Transplantation. 2005;79(10):1277-1286.

Knipe D, Howley P. Fields Virology. 5th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2006.

Limaye AP, Jerome KR, Kuhr CS, et al. Quantitation of BK virus load in serum for the diagnosis of BK virus-associated nephropathy in renal transplant recipients. J Infect Dis. 2001;(183):1669-1672.

Nickeleit V, Klimkait T, Binet IF, 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.

Scantlebury V, Randhawa P, Shapiro R, et al. Cidofovir: A Method of Treatment for BK Virus-Associated Transplant Nephropathy. Graft. 2002;5(suppl):S82-S87.

Vats A, Shapiro R, Scantelbury V, et al. BK Virus associated nephropathy and cidofovir: long term experience. [abstract]. Am J Transplant. 2003;3(suppl 5):A190.

PAO-02-0707 PCR tests are performed pursuant to a license agreement with Roche Molecular Systems, Inc.

Abstracts & Publications

Hamilton RS, Gravell M, Major EO. Comparison of Antibody Titers Determined by Hemagglutination Inhibition and Enzyme Immunoassay for JC Virus and BK Virus. J Clin Microbiol. 2000;38(1):105-109.

A comparison of antibody titers to JC virus (JCV) or BK virus (BKV) was made by hemagglutination inhibition (HI) and enzyme immunoassay (EIA) with 114 human plasma samples. Antibody titers to JCV or BKV determined by HI were lower than those determined by EIA. Nevertheless, as HI titers increased so did EIA titers. When antibody data were compared by the Spearman rank correlation test, highly significant correlations were found between HI and EIA titers. Results obtained by plotting EIA antibody titers for JCV against those for BKV generally showed a reciprocal relationship, i.e., samples with high antibody titers to JCV had lower antibody titers to BKV and vice versa. Some samples, however, had antibody titers to both viruses. Of the samples tested, 25.4% (25 of 114) had HI and EIA antibody titers to JCV and BKV which were identical or closely related. This is not the scenario one would expect for cross-reactive epitopes shared by the two viruses, but one suggesting that these samples were from individuals who had experienced infections by both viruses. Adsorption with concentrated JCV or BKV antigen of sera with high antibody titers to both JCV and BKV and testing by JCV and BKV EIA gave results which support this conclusion. Although 52.6% (51 of 97) of the samples from the Japanese population tested had very high antibody titers (>/=40,960) to either JCV or BKV, none of the samples were found by a dot blot immunoassay to have antibodies which cross-reacted with simian virus 40. The results from this study, in agreement with those of others, suggest that humans infected by JCV or BKV produce antibodies to species-specific epitopes on their VP1 capsid protein, which is associated with hemagglutination and cellular binding.

Stolt A, Sasnauskas K, Koskela P, Lehtinen M, Dillner J. Seroepidemiology of the human polyomaviruses. J Gen Virol. 2003;(84):1499-1504.

To assess the stability of polyomavirus antibodies in serial samples over time and the incidence and age-specific prevalence of polyomavirus infections, we established enzyme immunoassays (EIAs) using purified yeast-expressed virus-like particles (VLPs) containing the VP1 major capsid proteins of JC virus (JCV) and the AS and SB strains of BK virus (BKV). A random subsample of 150 Finnish women who had serum samples taken during the first trimester of pregnancy and had a second pregnancy during a 5 year follow-up period was selected, grouped by age of first pregnancy. The polyomavirus antibody levels were similar in samples taken during the first and second pregnancies (correlation coefficient 0.93 for BKV SB and 0.94 for JCV). Analysis of serum samples from 290 Swedish children aged 1-13 years, grouped by age in 2 year intervals, demonstrated that BKV seropositivity increased rapidly with increasing age of the children, reaching 98 % seroprevalence at 7-9 years of age, followed by a minor decrease. JCV seroprevalence increased only slowly with increasing age and reaching 72 % positivity among mothers >25 years of age. The age-specific seroprevalence of the human polyomaviruses measured using this VLP-based EIA was similar to previous serosurveys by other methods. The stability of the antibodies over time indicates that polyomavirus seropositivity is a valid marker of cumulative virus exposure, and polyoma VLP-based EIAs may therefore be useful for epidemiological studies of these viruses.