BK virus subtype correlation with viral loads in Western Australia

To the Editor,
BK virus (BKV) is a small, circular, double-stranded, non-enveloped DNA polyomavirus. The most common manifestation is BKV-associated nephropathy (BKVAN) in renal transplant patients. This can begin early (days) post-transplant, occurs in 1–10% of transplant patients, and ∼15% of patients with BKVAN experience graft loss.1 The mainstay of BKVAN management is cautious reduction in immunosuppression, so early diagnosis is critical. Definitive diagnosis of BKVAN is made by renal biopsy. However, as biopsies are invasive, most units perform surveillance through viral load assessments by quantitative polymerase chain reaction (qPCR) of urine and/or blood,2 with levels correlating with each other.3 The viral load in urine tends to rise earlier than plasma, with viruria usually preceding viraemia by 4 weeks.3 High level viraemia and viruria have both been associated with BKVAN.3 Sustained viral load >4 log10 copies/mL in plasma is considered presumptive evidence of BKVAN with urine viral load >7 log10 copies/mL a prompt to test plasma viral load and consider allograft biopsy.