Test ID: QCMV    
Cytomegalovirus, Molecular Detection, Quantitative PCR, Plasma

Early detection of cytomegalovirus (CMV) viremia

Monitoring CMV disease and response to viral therapy

Cytomegalovirus (CMV) is 1 of the most important infectious agents of transplant recipients, causing significant morbidity and mortality. Direct effects of infection include fever, leukopenia, hepatitis, colitis, and retinitis. Other manifestations of CMV infection in this population may be more subtle and include allograft injury and loss, increased susceptibility to infections with other organisms, and decreased patient survival (ie, indirect effects).(1) The risk of CMV disease in solid organ allograft recipients is highest in patients who have a negative CMV serostatus prior to transplantation, and receive an allograft from a CMV seropositive individual. Other factors, such as the type of immunosuppressive protocol, age of the recipient, and comorbidities, may also be associated with an increased risk of CMV disease.

Available diagnostic techniques for CMV include serology (which for transplant recipients is used to determine the pretransplant serologic status of the donor and recipient), viral culture (conventional tube culture and shell vial cell culture), antigen detection, and nucleic acid detection by PCR. Of these, PCR assays demonstrate the most sensitive and specific detection of CMV, while allowing for quantitative monitoring of CMV DNA levels in peripheral blood over time.

In general, higher viral loads are associated with tissue-invasive disease, while lower levels are associated with asymptomatic infection. However, there is a wide degree of overlap in viral load and CMV disease. For this reason, trends in viral load over time may be more important in predicting CMV disease than a single absolute value. Recommendations for serial monitoring of transplant recipients with quantitative CMV PCR have been published.(6,7) In general, changes of >0.5 log(10) may represent a biologically significant changes in virus replication.

None detected

A positive test result indicates the presence of cytomegalovirus (CMV) DNA; a quantitative value (copies/mL) is reported.

A result of "none detected" does not rule out the presence of CMV DNA (see Cautions).

This test should not be used as the only criterion to form a clinical conclusion; instead, results should be correlated with other test results, patient symptoms, and clinical presentation. The trend of viral loads over time may be more useful than a single absolute value for predicting the presence of cytomegalovirus (CMV) disease.

A result of "none detected" does not necessarily indicate the absence of CMV infection. False-negative results may be due to suppression of virus replication to levels below the detection threshold.

Some patients with tissue invasive disease may not have detectable viral load levels in peripheral blood. In these cases, qualitative detection of CMV DNA from tissue biopsy may provide useful adjunctive information.

This assay is only to be used for patients with a clinical history and symptoms consistent with CMV infection, and must be interpreted in the context of the clinical picture. This test should not be used to screen asymptomatic patients without risk factors for disease.

There is poor standardization between commercially available CMV PCR tests, and results from different institutions should not be directly compared. Quantitative results are best monitored using a single institution.

Inadequate specimen collection or storage may invalidate test results.

The following validation data support the use of this test for clinical testing.

Accuracy/Diagnostic Sensitivity and Specificity:

The original Mayo PCR assay contained probes and primers specific for the Hind IIIX region of the cytomegalovirus (CMV) virus. Roche later developed analyte specific reagents (ASR) for the UL54 gene of CMV. In comparison studies of 328 plasma specimens submitted for CMV testing, the sensitivity and specificity of the Roche CMV ASR was found to be 94% and 100% respectively, as compared to the previous Mayo Hind IIIX Mayo CMV assay.

Analytical Sensitivity/Limit of Detection (LoD):

In studies performed with spiked patient specimens, the sensitivity of the Roche ASR assay was shown to be approximately 1,000 targets/mL (whole virus in specimen matrix).

Analytical Specificity:

No PCR signal was obtained from extracts of 44 bacterial and viral isolates including Epstein-Barr virus, herpes simplex virus, varicella-zoster virus, human herpesvirus-6, human herpesvirus-7, human herpesvirus-8, and parvovirus.

Precision:

Both intraassay and interassay precision met acceptance criteria of <0.25 log copies/mL.

Reference Range:

The reference range is "None Detected" for this assay.

Reportable Range:

The reportable range of this assay is 2,000 to 200,000,000 copies/mL. Acceptable linearity is present between these levels.

1. Razonable RR, Paya CV, Smith TF: Role of the laboratory in diagnosis and management of cytomegalovirus infection in hematopoietic stem cell and solid-organ transplant recipients. J Clin Microbiol 2002;40(3):746-752

2. Razonable RR, Brown RA, Wilson J, et al: The clinical use of various blood compartments for cytomegalovirus (CMV) DNA quantitation in transplant recipients with CMV disease. Transplantation 2002;73(6):968-973

3. Schaade L, Kockelkorn P, Ritter K, Kleines M: Detection of cytomegalovirus DNA in human specimens by LightCycler PCR. J Clin Microbiol 2000;38:4006-4009

4. Mendez JC, Espy MJ, Smith TF, et al: Evaluation of PCR primers for early diagnosis of cytomegalovirus infection following liver transplantation. J Clin Microbiol 1998;36(2):526-530

5. Razonable RR, Brown RA, Espy MJ, et al: Comparative quantitation of cytomegalovirus (CMV) DNA in solid organ transplant recipients with CMV infection by using two high-throughput automated systems. J Clin Microbiol 2001;39(12)4472-4476

6. Humar A, Syndman D, The AST Infectious Diseases Community of Practice: Cytomegalovirus in solid organ transplant recipients. Am J Transplant 2009;9(S4):S78-S86

7. Kotton CN, Kumar D, Caliendo A, et al: International consensus guidelines on the management of cytomegalovirus in solid organ transplantation. Transplantation 2010;89(7):779-795