Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1343 page)

   Specimens should be collected early in acute infection.

   Urine is most often recommended for evaluation of neonates with suspected CMV infection. For evaluation of patients with suspected viremia, heparinized whole blood or isolated buffy coat cells are used to inoculate cultures.

   CMV is a fastidious virus and should be delivered to the laboratory as quickly as possible. Most specimens should be placed in a viral transport medium and transported at 4°C; do not freeze.

   Interpretation

   
Expected results:
Negative.

   
Negative results:
Negative cultures do not rule out CMV infection; they may be due to loss of viability after collection or low viral load in the specimen submitted.

   
Positive results:
Positive cultures usually indicate active CMV infection. Occasionally, positive cultures represent asymptomatic shedding of virus not associated with disease.

   Limitations

   Positive cultures may be due to asymptomatic shedding during latent infection; correlation with histopathology, and other clinical signs and symptoms may be needed to ensure specific diagnosis.

   Other Considerations

Viral culture may be used to provide a patient isolate for antiviral susceptibility testing or further characterization. CMV antigenemia studies or CMV viral load determination is more effective than viral culture for identification of early, preclinical CMV infection in transplant and other immunocompromised patients.

CYTOMEGALOVIRUS (CMV) QUANTITATIVE MOLECULAR ASSAY
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   Definition

   The CMV quantitative assay uses real-time PCR to quantitate CMV DNA extracted from plasma of CMV-infected individuals. The test quantifies CMV DNA over different ranges depending on the laboratory and assay methodology—for example 50–4,200,000 copies/mL. The first WHO International Standard for human cytomegalovirus (HCMV), NIBSC code 09/162, will help with standardization of nucleic acid amplification technique (NAT)-based assays for human CMV. The FDA-approved COBAS
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AmpliPrep/ COBAS
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TaqMan
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CMV Test has a range 1.37E+02–9.10E+06 IU/mL.