Cytomegalovirus PCR Quantitative
Cytomegalovirus (CMV) infections are a major cause of illness in immunocompromised adults and congenitally infected infants. Although the virus can be isolated from a variety of sources, viremia correlates best with clinically significant CMV disease. Detection of CMV viremia by standard culture techniques requires 3 to10 days. The introduction of specific antiviral therapy for CMV increased the need for rapid diagnostic tests. In 1998, the Roche Amplicor Qualitative PCR was adapted. This method utilized plasma samples and was much more specific for CMV disease than previous whole blood methods. In 2001, the Roche Cobas Amplicor CMV Monitor assay that can quantitate CMV viral load between 400 and 100,000 copies per mL of plasma was introduced. A comparative study of the qualitative and quantitative assays revealed that:
- Healthy individuals have <400 copies/ mL.
- Patients testing negative by qualitative PCR have <400 copies/mL. A negative qualitative result is very predictive of a negative quantitative result.
- Patients with positive qualitative PCR exhibited a very broad range of viral loads, varying from 1000 to >100,000 copies/mL. The quantitative assay is much more helpful in determining the clinical significance of CMV infection.
- Assay imprecision is ~30%, which is similar to quantitative HIV PCR assays. Serial results need to change more than this amount to be considered clinically significant.
Quantitative PCR is recommended to monitor transplant recipients for the development of CMV disease. Monitoring patients weekly after transplant with a quantitative CMV PCR assay can be used to guide preemptive therapy for CMV infection. Monitoring viral load after completion of therapy may be useful in predictive relapsing disease.
Specimen requirement is one lavender (EDTA) top tube of blood.
