What methods are used for Cytomegalovirus (CMV) testing?

Cytomegalovirus Testing Methods

CMV testing should be performed using quantitative PCR for DNA detection in immunocompromised patients, while serological testing for CMV-specific antibodies (IgM and IgG) is the first-line diagnostic approach for immunocompetent individuals with suspected CMV infection. 1

Testing Methods for CMV Detection

Molecular Methods

• Nucleic Acid Amplification Tests (NAAT)
  • Quantitative PCR for CMV DNA - Gold standard for immunocompromised patients 1
    • Specimen types depend on suspected site of infection:
      • Blood/plasma for systemic infection
      • Cerebrospinal fluid for CNS disease
      • Tissue biopsies for end-organ disease
      • Bronchoalveolar lavage for pulmonary involvement
  • Qualitative PCR - Used for detection in various specimens including CSF, urine, tissues, respiratory specimens, and body fluids 2

Serological Methods

• CMV-specific antibodies (IgM and IgG) - First-line test for immunocompetent individuals 1
  • Positive IgM with/without IgG indicates recent infection
  • IgG antibodies alone indicate past exposure/infection
  • False positive CMV IgM results may occur in patients with EBV infection 2

Antigen Detection

• CMV pp65 antigenemia test - Detection of viral proteins in peripheral blood leukocytes 2
  • Rapid results compared to culture (24-48 hours)
  • More sensitive than culture but less sensitive than PCR 3
  • Useful for preemptive treatment strategies in transplant recipients 2
  • May be difficult to perform during neutropenia 2

Viral Culture Methods

• Shell vial culture - More rapid than conventional culture (1-2 days vs up to 14 days) 2
• Conventional viral culture - Labor-intensive with long turnaround time (up to 14 days) 2
• Culture specimens include urine, saliva, blood, bronchoalveolar washings 2

Histopathology/Tissue Detection

• Immunohistochemistry - Detection of CMV antigens in tissue samples 2
• In situ hybridization - Detection of CMV nucleic acids in tissue samples 2
• Histopathologic examination - Looking for cytomegalic cells with intranuclear inclusions 2
  • Lower sensitivity compared to immunohistochemistry and PCR 2

Test Selection Based on Clinical Scenario

For Immunocompromised Patients

• Transplant recipients: Quantitative PCR for viral load monitoring; performed weekly from day 10 to day 100 post-transplant 1
• HIV patients: Quantitative PCR for monitoring CMV viremia 1
• Suspected end-organ disease: Tissue biopsy with immunohistochemistry or PCR from the affected organ 2

For Immunocompetent Individuals

• Suspected acute CMV infection: CMV-specific antibodies (IgM and IgG) 1
• Mononucleosis-like syndrome: CMV serology after negative heterophile antibody test 2

For Specific Organ Involvement

• CMV retinitis: Ophthalmoscopic examination (95% positive predictive value) 1
• CMV gastrointestinal disease: Endoscopy with biopsy for histopathology and immunohistochemistry 1
• CMV pneumonitis: Bronchoalveolar lavage with PCR or culture 1
• CMV neurologic disease: CSF PCR and brain imaging 1

Common Pitfalls in CMV Testing

• False negative PCR results may occur due to mutations in the target region of the CMV genome 4
• CMV pp65 antigenemia test cannot be performed when neutrophil counts are low 2
• Serum antigen and PCR tests do not always correlate with tissue infection, particularly in colonic CMV infection 2
• Positive CMV DNA in blood of immunosuppressed patients does not always indicate disease requiring treatment 1
• Haematoxylin and eosin staining for CMV inclusion bodies has poor sensitivity compared to immunohistochemistry and PCR 2

Test Interpretation

• Positive quantitative PCR in immunocompromised patients requires evaluation for preemptive therapy 2, 1
• Rising viral loads in transplant recipients may indicate need for antiviral treatment 1
• Positive IgG with negative IgM indicates past infection without current reactivation 1
• Positive IgM suggests recent primary infection 2, 1
• Positive tissue PCR or immunohistochemistry with compatible clinical symptoms confirms end-organ disease 2

By selecting the appropriate testing method based on the clinical scenario and patient's immune status, clinicians can accurately diagnose CMV infection and initiate appropriate management strategies to reduce morbidity and mortality.