A real-time quantitative CMV PCR assay (qCMV) will be available from the University of Minnesota, Fairview Clinical Virology Laboratory beginning December 12th. Physicians will have the option of ordering this new assay or the CMV pp65 antigenemia test until approximately March 1, 2006, at which time the antigenemia test will be discontinued.
In order to provide smooth continuity in managing patients whose CMV pp65 antigenemia test is positive, our laboratory will perform both assays on the same sample upon request. This should permit calculation of a conversion factor to compare the level of antigenemia (positive cells per 50,000 leukocytes) with CMV DNA copy numbers.
Why are we switching? The CMV antigenemia assay is a very sensitive and specific test for CMV infection. However, specimens must contain a certain number of leukocytes with intact morphology to be read properly. Specimens from leukopenic patients and samples requiring prolonged storage or shipping may not be suitable for accurate quantitation. The viral DNA required for the qCMV assay is more stable and does not require intact cellular morphology for quantitation. In addition, preliminary studies in our laboratory suggest that the qCMV is more sensitive than the pp65 antigenemia test.
The specimen of choice will be whole blood (as is the case with EBV) but plasma or peripheral blood leukocyte fractions may also be requested.