What is the role of quantitative polymerase chain reaction (PCR) in the workup of cytomegalovirus (CMV) infection?

Updated: Jul 07, 2021
  • Author: Ricardo Cedeno-Mendoza, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Quantitative PCR has been used to detect plasma CMV. The advantage of quantitative PCR over regular PCR is unknown. Ideally, quantitative PCR is as sensitive as qualitative PCR and provides an estimate of the number of CMV genomes present in plasma.

A study of newborns compared real-time PCR assays of liquid-saliva and dried-saliva specimens with rapid culture of saliva specimens obtained at birth. Both PCR assays showed high sensitivity and specificity for detecting CMV infection. [54]

A study of more than 3400 blood specimens from organ transplant recipients tested with CMV PCR and pp65 antigenemia found that quantitative real-time PCR for CMV DNA could be used in lieu of antigenemia for monitoring CMV infection and determining when to initiate preemptive treatment. [55]

In theory, the CMV viral load would indicate whether therapy is necessary because patients whose viral load is below a certain cutoff would not develop CMV disease. However, the level of viremia necessary for CMV disease to occur may vary depending on host factors and the type of organ transplant, and this may need to be determined empirically. For example, in CMV retinitis, the viral load has a poor positive predictive value, meaning its clinical utility is limited. A detectable CMV viral load at the time of CMV retinitis diagnosis was shown in one study to correlate with increased mortality (P = 0.007). [56] CMV involvement of the GI tract also has a poor correlation with CMV viremia.

Commercially available quantitative PCR assays include the COBAS Amplicor CMV Monitor test (Roche Diagnostics, Indianapolis, IN) and various laboratory-developed PCR assays. The COBAS Amplicor CMV Monitor test measures viremia in the range of 600-100,000 copies/mL. [57]

In the quest to standardize viral load testing for CMV, the FDA approved marketing in July 2012 of a fully automated assay, the COBAS AmpliPrep/COBAS TaqMan CMV test (CAP/CTM CMV test, Roche Molecular Diagnostics, Pleasanton, CA), which uses an international standard to quantitate plasma CMV load. This assay is available in Europe, but not yet in the United States. It measures viremia in a range of 150-10,000,000 copies/mL. [58]

Because viral loads are not comparable among different assays, it is important to use the same test and same sample type (whole blood or plasma) when monitoring patients over time. [59]

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