What tests should I order for serology to check for Cytomegalovirus (CMV) and BK virus?

Diagnostic Testing for CMV and BK Virus in Transplant Recipients

For monitoring CMV and BK virus infections in transplant recipients, you should order quantitative plasma nucleic acid testing (NAT) for both viruses, as this is the most sensitive and specific method for detection and monitoring of these infections.

CMV Testing

Initial Testing and Monitoring

• For CMV, order quantitative CMV DNA testing by NAT (viral load) in plasma or whole blood 1
• CMV serology (IgG and IgM antibodies) is recommended as first-line testing only in immunocompetent individuals suspected of having acute CMV infection, not for transplant recipients 1
• In transplant recipients, CMV viral load by NAT is preferred over antigenemia testing as it is more sensitive and has become the standard of care 1

Monitoring Schedule for CMV

• Weekly monitoring of CMV by NAT or pp65 antigenemia in patients with CMV disease 1
• Continue therapy until CMV is no longer detectable by plasma NAT or pp65 antigenemia 1
• For transplant recipients on prophylaxis, CMV testing should be performed whenever there is an unexplained rise in serum creatinine 1

BK Virus Testing

Initial Testing and Monitoring

• For BK virus, order quantitative BK virus DNA testing by NAT (viral load) in plasma 1
• Urine testing for BK virus may be used as a screening test but is less specific than plasma testing due to common viral shedding in urine 1
• BK virus DNA quantification in plasma provides an early indication of BK virus-associated nephropathy 1

Monitoring Schedule for BK Virus

• Monthly screening for the first 3-6 months after transplantation 1
• Every 3 months until the end of the first post-transplant year 1
• Whenever there is an unexplained rise in serum creatinine 1
• After treatment for acute rejection 1

Important Considerations

Specimen Collection and Transport

• For both CMV and BK virus NAT:
  • Collect whole blood in EDTA tubes 1
  • Transport at room temperature 1
  • Optimal transport time is less than 2 hours 1

Clinical Interpretation

• For BK virus, a plasma viral load persistently greater than 10,000 copies/ml (10^7 copies/L) indicates a need for reduction in immunosuppressive medications 1
• For CMV, viral load testing is used as a marker for preemptive therapy, to diagnose CMV-associated signs and symptoms, and to monitor response to antiviral therapy 1

Potential Interactions

• Be aware that CMV viremia may be associated with a decreased incidence of BK virus reactivation after kidney transplantation 2
• This protective effect may be due to reduction in immunosuppression after diagnosis of CMV viremia 2

Pitfalls to Avoid

• Do not rely on serology (IgG/IgM) testing alone for CMV in transplant recipients, as it has poor sensitivity and specificity in this population 3, 4
• Avoid urine testing as the sole method for BK virus detection due to risk of specimen cross-contamination and false positives from high levels of virus in urine 1
• Remember that each institution must establish its own threshold for identifying patients at highest risk of BK virus-associated nephropathy, as there are no FDA-cleared quantitative NAATs with standardized thresholds 1

By following these testing recommendations, you will be able to effectively monitor for and detect CMV and BK virus infections in transplant recipients, allowing for timely intervention to prevent complications and graft dysfunction.