- Last Update On : 2012-12-24
BK is a type of polyomavirus that is ubiquitous in nature and infects most people in early childhood. Seroprevalence is 60-100% in epidemiologic studies. Following primary infection, the virus becomes latent in lymphocytes and renal epithelium. Intermittent viral shedding may occur in immunocompetent individuals (up to 20% incidence) and more frequently in immuno-compromised individuals (up to 60% incidence). BK is so-named from the initials of the patient from whom the virus was first isolated. A related polyomavirus that infects humans is JC virus, which is associated with progressive multifocal leukoencephalpathy.
BK virus reactivation is a major concern for renal transplant and bone marrow transplant recipients. Following reactivation, BK virus either clears spontaneously, perisists in urine, or progresses to viremia. Reactivation has been linked to tubulointerstitial nephritis and nephropathy as well as ureteral stenosis in renal transplant patients, while bone marrow transplant patients are at risk for hemhorragic cystitis. BK virus associated nephropathy is an important cause of allograft failure and affects renal transplant patients an average of 44 weeks post-transplant. Increasing degrees of immunsuppression are associated with increased risk for BK reactivation.
Quantitative PCR for BK virus DNA in blood or urine specimens is useful for monitoring and diagnosis of BK-associated complications in transplant recipients. In general, the levels of urinary BK virus DNA are 100 to 1000-fold higher than in blood, and the presence of urinary BK virus DNA precedes detection in blood specimens. Increasing viral load and sustained viremia have been associated with development of nephropathy post-renal transplant.
Urine is the specimen of choice for initial BK virus testing as positivity may provide early evidence of infection. When both blood & urine specimens are submitted for testing, urine is tested first. If urine tests positive for BK virus, the blood specimen will be tested in the following run. If the urine tests negative for BK virus, blood testing is canceled. If a patient has previously had a blood sample positive for BK virus, both specimens will be tested.
The lower reportable range is 500 copies per mL. Specimen requirement is 1mL EDTA plasma or 1mL urine from a random collection. Turnaround time is 48 hours or less.