Serum

Preferred Minimum: 0.5 mL serum
Absolute Minimum: 0.15 mL serum

Submit specimen to laboratory as soon as possible after collection.

1-8 days upon receipt at reference laboratory

0.50 Index or less: Low Avidity
0.51-0.59 Index: Intermediate Avidity
0.60 Index or greater: High Avidity

Identifying CMV infections in pregnant women during the first trimester is of significant importance for clinical care. Acute infection is typically characterized by increased CMV-specific IgM and IgG antibodies. However, CMV IgM antibodies may persist for several months or even years after initial infection, which limits their utility in the accurate diagnosis of recent CMV infection. CMV IgM antibodies can also be detected during viral reactivation, thus complicating the diagnosis of a recent primary infection. Therefore, measuring IgG antibody avidity to CMV antigens can aid in discriminating recent from prior CMV infections. Index values of 0.5 or less generally indicate recent infection (within the previous 3 to 4 months). However low avidity values cannot exclude the possibility of persistent IgG antibodies with low avidity. Index values of 0.6 or greater indicate an infection occurring more than 3 months prior to testing. Because IgG avidity testing for CMV after the first trimester is not easily interpreted, detection of high avidity CMV IgG antibodies during the first trimester (12 to 16 weeks gestation) helps exclude a diagnosis of an acute CMV infection post-conception.

Order to aid in the diagnosis of cytomegalovirus (CMV) infection during pregnancy after initial testing for CMV IgM and IgG has been performed.

Discrimination between recent (primary) and past cytomegalovirus (CMV) infection can be an important tool in the clinical management of transplant recipients and pregnant women. Although nearly all individuals with recent CMV infection are positive for CMV IgM, individuals with past CMV may also express CMV IgM following viral reactivation; thus, detection of CMV IgM is not a reliable indicator of recent infection. Measurement of CMV IgG avidity can assist in discriminating recent from past CMV infection. Although a low avidity index is a reliable indicator of CMV infection within the previous 6 months, a high avidity index is more meaningful from a clinical standpoint; a high avidity index essentially excludes the possibility that infection occurred within the previous 4 months.

In summary, assessment of CMV-specific IgG avidity is an extremely powerful tool for estimating the time of CMV infection. Such information is particularly important in the clinical management of pregnant women found to be positive for CMV antibodies at their first prenatal visit. Determining the time of primary infection can help guide decisions regarding antiviral therapy by identifying those women who should or should not be treated during pregnancy. CMV IgG avidity measurement also has broad applicability to the management of other patient groups with an increased risk of debilitating CMV disease, such as solid organ transplant recipients. Approximately 50% of pregnant women with primary CMV infection transmit CMV to their infants. Measuring CMV IgG avidity can reliably distinguish primary infection from active latent infection during pregnancy.

Semi-Quantitative Enzyme-Linked Immunosorbent Assay

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