Laboratory method | Sample used for testing | Reported sensitivity (percent)* | Reported specificity (percent)* | Comments |
Viral culture | Urine or saliva obtained within first 3 weeks of life | 100 | 100 | Traditional reference standard. |
Detects CMV based on cytopathic changes in cell culture with fibroblast cell lines. | ||||
Usually positive within 1 to 3 days of incubation but may take up to 28 days before a negative result is declared. | ||||
Disadvantages include: relatively long time required to detect the virus, labor- and resource-intensive, and requires tissue culture facilities. | ||||
Rapid culture (also called shell vial assay or shell vial culture)¶ | Urine or saliva obtained within first 3 weeks of life | 92.3 to 100 | 100 | Enhanced culture method using centrifugation and staining for early antigen production. |
Allows for identification of the virus within 24 hours. | ||||
Advantage over standard viral culture is that it is rapid, simple to perform, and less expensive. | ||||
False-positive results may occur due to retained CMV antigen on the shell vial monolayer, producing a low-positive result. | ||||
A confirmatory test (either viral culture or PCR) should be performed to establish the diagnosis of congenital CMV. | ||||
PCR¶ | Urine or saliva obtained within first three 3 of life | 97.4 to 100 | 99.9 | Detects CMV DNA in the urine or saliva. |
Advantages over standard and shell vial culture techniques include: rapid turnaround, does not require live virus for detection of CMV and thus is not affected by storage and transport conditions, and lower cost. | ||||
Available in many hospital-based and reference laboratories. | ||||
Occasional false-positive results occur; we suggest confirming positive tests with repeat PCR on urine or saliva or both. | ||||
Newborns with congenital CMV infection shed large quantities of CMV from both urine and saliva for prolonged periods; therefore, these tests should be positive repeatedly. | ||||
PCR | Dried blood spot | 34 to 77 | 99.9 | Detects CMV DNA in the dried blood spot obtained for newborn screening. |
Allows retrospective diagnosis of congenital CMV infection. | ||||
Not all infected infants are viremic at birth, accounting for low sensitivity of this test compared with PCR in urine or saliva samples. | ||||
Available in research or public health laboratories (CDC). | ||||
Quantitative PCR (CMV DNAemia) | Whole blood or plasma | N/A | N/A | Measures amount of CMV DNA in the blood. |
Used for monitoring infants during therapy; not used for establishing the diagnosis of congenital CMV. | ||||
Preferred over CMV antigenemia for quantitative measurement of viremia. | ||||
CMV antigenemia | Blood | N/A | N/A | Detects CMV proteins (pp65) in peripheral blood leukocytes. |
Not recommended in the diagnostic evaluation of infants with congenital CMV. | ||||
Serology | Blood | N/A | N/A | Not recommended for routine diagnosis of congenital CMV. |
Presence of CMV IgG antibody in the newborn may only reflect passive transfer of maternal antibody; however, its absence makes CMV infection very unlikely. | ||||
CMV IgM antibody in the newborn is insensitive and may be falsely negative in over one-half of infected newborns. |
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