Tests for CMV Infection
The recommended test for diagnosing CMV infection depends on the patient's immune status: CMV-specific IgM and IgG antibodies are first-line for immunocompetent patients, while quantitative nucleic acid testing (QNAT) for CMV DNA viral load is the preferred method for immunocompromised patients including transplant recipients. 1
Testing Strategy by Patient Population
Immunocompetent Patients
For immunocompetent individuals with suspected acute CMV infection:
- CMV-specific antibody testing (serology) is the first-line diagnostic test 1
- IgM antibodies indicate recent infection, though false positives can occur with EBV infection or other immune activation 1
- IgG antibodies alone indicate past exposure to CMV 1
Important caveat: CMV IgM has limited specificity and can produce false positives in patients with EBV or activated immune systems from other causes 1
Immunocompromised Patients (Transplant Recipients)
For organ or stem cell transplant recipients, the testing approach is fundamentally different:
- CMV DNA quantitative nucleic acid testing (QNAT) is the preferred technique for managing CMV infection 2
- Measure CMV DNA load in peripheral blood (whole blood or plasma specimens are equally suitable) 2
- Use for preemptive therapy decisions, diagnosing CMV-associated symptoms, and monitoring treatment response 1
- pp65 antigenemia assay is less sensitive but acceptable if QNAT is unavailable 2
Key technical point: Assays calibrated to international units (IU) using WHO standards are recommended to reduce inter-assay variability, though some commercial assays still deviate by 1.5 log IU/mL or more 2
Congenital CMV Infection
For newborns with suspected congenital infection:
- Urine culture for CMV continues to be used at some institutions because viral load is typically high and CMV is shed in urine of newborns 1
- CMV PCR in urine or saliva for neonatal diagnosis 3
- Dried blood spots on Guthrie cards for retrospective diagnosis 3
Pre-Transplant Screening
Before allogeneic hematopoietic cell transplantation:
- CMV serological status must be assessed in all patients and donors 2
- This remains the most important predictor of CMV reactivation post-transplant 2
- Strongly influences donor selection and outcomes 2
Specimen Types and Transport
According to IDSA/ASM guidelines 1:
For CMV DNA quantification (viral load):
- Cerebrospinal fluid in sterile container, room temperature, <2 hours
For CMV DNA detection (qualitative):
- CSF, urine, tissues, respiratory specimens, body fluids in sterile container, room temperature, <2 hours
For culture:
- Urine in sterile container, room temperature, <2 hours
Tests to Avoid or Use with Caution
Culture-based assays have significant limitations:
- Labor-intensive and can take up to 14 days (shortened to 1-2 days with shell vial assay) 1
- Poor sensitivity compared to molecular methods 1
- Now largely replaced by QNAT in most settings 4
CMV antigenemia (pp65) assay:
- Being performed by fewer laboratories as NAATs gain favor 1
- Sensitivity 89.18%, specificity 100% 5
- Still acceptable when QNAT unavailable 2
Advanced Testing Considerations
Monitoring Kinetics in High-Risk Patients
Kinetic analyses of plasma CMV DNA loads (e.g., CMV DNA doubling time) can guide preemptive treatment initiation 2:
- Viral DNA load doubling time <2 days predicts eventual need for preemptive therapy 2
- Timely initiation reduces overall antiviral therapy days, side effects, and progression to CMV disease 2
Antiviral Resistance Testing
For immunocompromised patients with suspected drug resistance:
- Sequencing of UL97 (phosphotransferase gene) with or without UL54 (DNA polymerase gene) 1
- Performed on DNA amplified directly from clinical specimens 1
Tissue Diagnosis
When tissue-based diagnosis is needed:
- CMV antigens demonstrated by immunohistochemical or in situ hybridization on formalin-fixed, paraffin-embedded tissues 1
- CMV DNA by NAAT in various clinical specimens may be useful for diagnosing CMV disease 1