BK Virus Screening and BK Nephropathy
The human polyomavirus BK (BKV) is a latent DNA virus that resides in the uroepithelium and can reactivate under immunosuppression. BK nephropathy (BKN) develops in up to 10% of kidney transplant recipients and accounts for 15–50% of allograft losses.
- Screening Strategy and Frequency
Regular screening is essential because BK viremia typically appears ~8 weeks before kidney injury becomes detectable.
- Preferred Method:
Quantitative plasma nucleic acid testing (NAT) is the most sensitive method for detecting BKV infection and identifying high-risk patients. - Alternative Method:
If NAT is unavailable, urine cytology for decoy cells is acceptable, though it has a low positive predictive value for BKN. - Standard Schedule:
– Monthly for the first 3–6 months post-transplant
– Every 3 months until the end of the first year - Clinical Triggers:
Additional testing is required when:
– Serum creatinine rises without explanation
– After treatment for acute rejection
- Diagnosis of BK Nephropathy
High viral loads suggest risk, but definitive diagnosis requires histology.
- Biopsy Requirements:
Suspected BKN must be confirmed by renal allograft biopsy with staining for SV40 large T antigen. - Tissue Sampling:
Because BKV infection is often patchy and affects the renal medulla, two biopsy cores including medullary tissue are recommended.
- Management and Treatment
There is no proven antiviral therapy for BKN. Management focuses on adjusting immunosuppression.
- Intervention Threshold:
Reduction of immunosuppression is suggested when plasma BKV load persistently exceeds
10⁴ copies/mL (10,000 copies/mL). - Immunosuppression Adjustment:
Typical steps include:
– Stopping anti-proliferative agents (MMF or azathioprine)
– Lowering calcineurin inhibitor (CNI) target levels - Specific Agents:
Drugs such as leflunomide, cidofovir, or quinolones have shown antiviral activity in small studies, but no strong evidence supports their superiority over immunosuppression reduction alone.
- Prognosis and Retransplantation
Loss of a graft due to BK nephropathy does not prevent future transplantation.
Re-transplantation is considered safe, and no special precautions—including allograft nephrectomy—are routinely required.
